global dimensioning and tolerancing addendum (gd&t) – 2004

ENGINEERING STANDARDS

Design Standard Electronic C2B

Global Dimensioning And Tolerancing Addendum – 2004

© Copyright 2004 General Motors Corporation All Rights Reserved

October 2004 Originating Department: North American Engineering Standards of 59

Contents Foreword…………………………………..2

GM Acknowledgement…………………....2

Automotive Industry Representative

Acknowledgment……………...…………..2

Structure………………………………..….2

General Motors Authorization…………….2

Figures…………………………………….3

Titleblock Notes…………..…………….…3

Section 1

Scope, Definitions, and General

Dimensioning

1.3 Definitions……………………………..4

1.4 Fundamental Rules…………………….7

1.5 Units of Measurement…………………8

1.6 Application of Dimensions……………8

1.7 Dimensioning Features………………..8

1.8 Location of Features……………….….9

Section 2

General Tolerancing and Related Principles

2.7 Limits of Size…………………..…….25

2.8 Applicability of RFS, MMC, and

LMC………………………………..…….26

2.15 Radius………………………………27

2.16 Statistical Tolerancing……..……….27

2.17 Uniform Thickness/Gap Toler-ance…………………………………27

Section 3

Symbology

3.3 Symbol Construction………………...32

3.5 Feature Control Frame Placement…...32

Section 4

Datum Referencing

4.2 Immobilization of Part………..……...35

4.4 Specifying Datum Features in an

Order of Precedence………...…….……...35

4.5 Establishing Datums…………………35

4.6 Datum Targets………………………..37

4.7 Restraining Datum Features………….37

4.8 Restraining Conditions…………….…38

Section 5

Tolerances of Location

5.3 Fundamental Explanation of Positional Tol-erancing………………………………50

5.11 Coaxiality Controls…………………51

5.12 Concentricity………………………..51

5.14 Symmetry Tolerancing……………...51

5.16 Cylindrical Part with Bends………...51

Section 6

Tolerances of Form, Profile, Orientation, and Runout

6.5 Profile Control……………………….53

6.6 Orientation Tolerances……………….54

6.8 Free State Variation………………….54

APPENDIX B

Formulas for Positional Tolerancing

B1 General……………………………….57

Appendix New F

Effect of Changes to the Definition of Actual Mating Envelope on the Figures in Y14.5

F1 General………………………………..57

C2B GM ENGINEERING STANDARDS


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Foreword

General Motors Corporation and Delphi Corpora-tion have adopted an amended version of the ASME Y14.5M-1994 dimensioning and toleranc-ing standard (amended by this addendum) for use by the above companies on all product engi-neering documentation.

This addendum was created to address the fol-lowing areas:

1. Select an option from ASME Y14.5

2. Clarify a concept from ASME Y14.5 3. Discourage/disallow the use of a concept

from ASME Y14.5 4. Include a concept not covered by ASME

Y14.5

All other standards referenced in ASME Y14.5 have not necessarily been adopted by the above companies, and are not automatically invoked. Current company standards will take precedence unless otherwise noted. GM Acknowledgment

This document represents the consensus of the members of the GM GD&T Task Team.

GM GD&T contributing members:

Michael A. Murphy, GMPT

Robert Bourland, GMPT

Guy Browne, Holden

Thomas Drexler, Opel

Anders Gustavsson, Saab

James Gyomber, Holden

Gisela Herzing, GM Ruesselsheim

Alex Krulikowski, GMPT

Dale MacPherson, GMPT

Cliff McCord, NAVO

Tibor Nuebl, Opel

Hans-Olof Svensson, Saab

Susan Belloli, GMPT

Klaus W. Schulz, Opel Powertrain GmbH

Andy Watts, NAVO

Duane Harbowy, GMPT

Automotive Industry Representative Ac-knowledgment

This addendum also represents input of the following automotive industry representatives:

Neil Freson, Delphi Energy & Chassis Systems

Paul Sams, Delphi Delco Electronics Systems

Dave Arnold, Delphi Safety & Interior Systems

James Anderson, Delphi Harrison Thermal Sys-tems

Bruce Eggert, Delphi Harrison Thermal Systems

Dan Meyers, Delphi Delco Electronics Systems

Jamie Florence, Aerotec (figure construction)

General Motors Authorization

This standard is authorized by the GM Global Engineering Design Committee Notice of Action # GEDC 162. Structure

The paragraph numbering in this addendum is as follows: Paragraphs are generally numbered to coincide with numbers in ASME Y14.5. Para-graph numbers preceded by “NEW” are addi-tions to Y14.5. Unless otherwise noted, para-graphs not preceded by “NEW” replace the paragraph in Y14.5 that is identified by the same number. Italicized text may be added, following the paragraph title noting whether the paragraph is a deletion or to describe the changes to an existing paragraph in Y14.5. Paragraph refer-ences noted in the figures refer to the para-graphs contained in this document. Figures ref-erenced in the text but not shown in this adden-dum are found in Y14.5.

Paragraph titles contained in parenthesis are for index referencing only and do not reflect changes to Y14.5.

The words “shall/must/required” describe strict requirements. Procedural steps defined by these words must be followed.

The words “should/preferred/recommended” describe preferences. Procedural steps defined by these words must be followed whenever there is no valid reason to do otherwise.

The words “acceptable/allowed/may/might” grant permission. They do not require or recommend the practice they specify; neither do they forbid or discourage alternative practices.

GM ENGINEERING STANDARDS C2B


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Figures

The figures in this Addendum exhibit the arrow method of view projection. GM Engineering Standards – Drawing Views and Sections (C3) Titleblock Notes

The note shown in Fig. F-1 shall appear on drawings, documents or within databases which are in accordance with the General Motors Global Dimensioning and Tolerancing Adden-dum – 2004. The note shall be in the title block (or in the general notes). The note invokes this addendum.

THIS DOCUMENT IS IN ACCORDANCE WITH ASME Y14.5M-1994 AS AMENDED BY THE GM GLOBAL DIMENSIONING AND TOLERANCING ADDENDUM – 2004.

Figure F-1 – Note To Invoke Gm Global Dimensioning And Tolerancing Addendum – 2004



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1 Scope, Definitions, and General Dimensioning

1.3 Definitions.

1.3.3 Datum. A theoretically exact point, axis, line, or plane derived from the true geometric counterpart. A datum is the origin from which the location or geometric characteristics of fea-tures of a part are established.

1.3.5 Datum Feature Simulator. A surface of adequately precise form (such as a surface plate, a gage surface, fixture pad, pin, centering device, or a mandrel) used to establish the simu-lated datum(s).

Note: Datum feature simulators are used as the practical embodiment of the datums during manufacture and inspection.

1.3.7 Datum Target. A specified point, line, or area on a drawing that represents a theoretically perfect fixture element.

1.3.9 Dimension, Basic. A numerical value used to describe the theoretically exact size, profile, orientation, or location of a feature; orien-tation or location of feature of size; or datum target. See Fig. 3-7. It is the basis from which permissible variations are established by toler-ances on other dimensions, in notes, or in fea-ture control frames. See Figs. 2-14, 2-15, and 3-25. Title block or general plus/minus tolerances do not apply to basic dimensions.

1.3.11 Envelope, Actual Mating. A general term used to refer to an unrelated or related actual mating envelope.

Note: Changes to the definition of Actual Mating Envelope have had numerous effects on figures in Y14.5. Appendix NEW F outlines the effects on figures in Y14.5.

1.3.11.1 Envelope, Unrelated Actual Mating. An unrelated actual mating envelope, (unrelated to a datum reference frame), can be either external or internal as described below:

(a) For an external feature of size, a similar per-fect feature counterpart of smallest size that can be circumscribed about the feature of size so that it contacts the surface or surfaces. For example, a smallest cylinder of perfect form or two parallel planes of perfect form at minimum separation that contacts the surface(s). See Fig. 1-57.

(b) For an internal feature of size, a similar per-fect feature counterpart of largest size that can

be inscribed within the feature of size so that it contacts the surface or surfaces. For example, a largest cylinder of perfect form or two parallel planes of perfect form at maximum separation that contacts the surface(s).

1.3.11.2 Envelope, Related Actual Mating. A related actual mating envelope, (related to a datum reference frame), can be either external or internal as described below: (a) For an external feature of size datum feature, a similar perfect feature counterpart of smallest size that can be circumscribed about the feature of size so that it contacts the surface or sur-faces. For example, the smallest cylinder of perfect form or two parallel planes of perfect form at minimum separation that contacts the surface(s). This envelope is oriented relative to the appropriate datum(s), See Fig. 1-57.

(b) For an internal feature of size datum feature, a similar perfect feature counterpart of largest size that can be inscribed within the feature of size so that it contacts the surface or surfaces. For example, the largest cylinder of perfect form or two parallel planes of perfect form at maxi-mum separation that contacts the surface(s). This envelope is oriented relative to the appro-priate datum(s).

1.3.12.1 Feature, Interrupted. A feature, (sur-face), that has an interruption. The keyword INTERRUPTED is placed adjacent to a size dimension, feature control frame or the datum feature symbol indicating that the specified toler-ance zone, size dimension or datum feature applies through the interruption. See fig. 1-59.

1.3.13 Feature of Size, Axis Of. A straight line that coincides with the axis of the unrelated ac-tual mating envelope of a feature of size. See Fig. 1-57.

1.3.14 Feature of Size, Center Plane Of. A plane that coincides with the center plane of the unrelated actual mating envelope of a feature of size.

1.3.15 Feature of Size, Derived Median Plane Of. An imperfect plane (abstract) that passes through the center points of all line segments bounded by the feature of size. These line seg-ments are normal to the unrelated actual mating envelope.

1.3.16 Feature of Size, Derived Median Line Of. An imperfect line (abstract) that passes through the center points of all cross sections of the feature of size. These cross sections are



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normal to the axis of the unrelated actual mating envelope. The cross section center points are determined as per ANSI B89.3.1.

1.3.17 Feature of Size. A general term used to refer to a whole or interrupted feature of size.

1.3.17.1 Whole Feature of Size. A single cylindrical or spherical surface, or circular element, or a pair of parallel surfaces or elements, that may be truncated or have an obstruction or recess that satisfies one of the following conditions: (a) A circular element associated with a dia-metral limit or plus and minus dimension that may have one or more obstructions or recesses. Any obstruction or recess must be less than 180 degrees of rotation around the axis. See Fig. 1-70

(b) A cylindrical surface associated with a dia-metral limit or plus and minus dimension that may be truncated or have one or more obstruc-tions or recesses, (for example: drilled holes, keyway, partial spline shaft, partial thread, partial groove, partial bead, etc.),. Any obstruction or recess must be less than 180 degrees of rotation around the axis. See Figs. 1-62 and 1-63.

(c) A spherical surface associated with a dia-metral limit or plus and minus dimension that may have one or more obstructions or recesses, (for example: drilled holes, partial groove, partial bead, etc.),. Any obstruction or recess must be less than a hemisphere. See Fig. 1-71 (d) A helical surface associated with a diametral limit or plus and minus dimension, such as a major diameter of an external thread or minor diameter of an internal thread,. See Fig. 1-72 (e) A set of two opposed point elements associ-ated with a limit or plus and minus

dimension. The associated dimension defines the variation of the length of a line segment ter-minating at the point elements. See Fig. 1-58(a).

(f) An opposed point and line element, associ-ated with a limit or plus and minus

dimension. The associated dimension defines the variation of the length of a line segment ter-minating at the point and line elements, and normal to the line element. See Fig. 1-58(b).

(g) An opposed point and a planar surface that may have an obstruction or recess, (for exam-ple: drilled holes, partial groove, partial bead, etc.), associated with a limit or plus and minus dimension. The associated dimension defines

the variation of the length of a line segment ter-minating at the point element and planar surface, and normal to the planar surface. See Fig. 1-58(c).

(h) A set of two opposed parallel line elements, associated with a common limit or plus and mi-nus dimension. The associated dimension de-fines the variation of the length of a line segment terminating at, and normal to the opposed line elements. See Figs. 1-66, 1-67(b) and 1-58(d).

(i) An opposed parallel line element and planar surface associated with a common limit or plus and minus dimension that may have an obstruc-tion or recess, (for example: drilled holes, partial groove, partial bead, etc.),. The associated di-mension defines the variation of the length of a line segment terminating at the line element and planar surface, and normal to the opposed ele-ments. See Figs. 1-67(b) and 1-58(e).

(j) A set of two opposed parallel surfaces asso-ciated with a common limit or plus and minus dimension, each of which may have an obstruc-tion or recess, (for example: drilled holes, key-way, partial spline shaft, partial thread, partial groove, partial bead, etc.),. The associated di-mension defines the variation of the length of any line segment terminating at, and normal to the opposed parallel surfaces. See Figs. 1-74, 1-58(f).

1.3.17.2 Feature of Size, Interrupted. A fea-ture of size that has an interruption in one of the associated features or elements. The keyword INTERRUPTED is placed adjacent to the size dimension, tolerance or datum feature symbol indicating that the specified tolerance zone, size dimension or datum feature applies through the interruption. For circular elements and cylindri-cal surfaces any recess or obstruction must be less than 180 degrees of rotation around the axis. See Figs. 1-59(a) and(b), 1-60, 1-64, 1-65 and 1-74.

1.3.26.1 Size, Unrelated Actual Mating Envelope. The value of the unrelated actual mating envelope. See Fig. 1-57.

1.3.26.2 Size, Related Actual Mating Enve-lope. The value of the related actual mating envelope. See Fig. 1-57.

1.3.35 True Geometric Counterpart. The theo-retically perfect boundary of a feature of size datum feature virtual condition for LMC or MMC applications, datum target, unrelated actual mat-ing envelope for RFS primary datum features or



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related actual mating envelope for RFS secon-dary or tertiary datum features or best-fit (tan-gent) plane for planar datum features. See Figs. 4-11, and 4-10. Also see paras. 1.3.2 and 1.3.3 regarding the simulated datum.

1.3.38 Free State. The condition where no forces other than gravity are applied.

1.3.39 Restrained. The condition where forces in addition to gravity are applied.

1.3.40 Element. A point, line, or arc derived from a surface. The length of the element is con-strained by the bounds of the part surface.

1.3.41 Opposed Elements. A general term used to refer to elements as described in paragraphs 1.3.16.1 and 1.3.16.2.

1.3.41.1 Opposed Point Elements. Two (2) point elements, A and B, are opposed if the fol-lowing conditions apply: Vectors originating and extending from points A and B that are coinci-dent to a line through points A and B, and di-rected away from the material, must be in oppo-site directions and normal to the surfaces from which the point elements are derived. When both points lie on the same line element other than line end points, or planar surface other than the surface edges, they shall not be considered opposed elements. See Fig. 1-58(a).

1.3.41.2 Opposed Point and Line Element. A point element A and a line element B are op-posed if the following conditions apply: Vectors originating and extending from point A and line B that are coincident to a line through point A and normal to line B, and directed away from the material, must be in opposite directions and normal to the surfaces from which the point and line elements are derived. The elements are opposed if a vector originating and extending normal from line element B intersects point A. When the point element and line element lie on the same line or both elements lie on the same planar surface, other than the surface edges, they shall not be considered opposed elements. See Fig. 1-58(b).

1.3.41.3 Opposed Point Element and Planar Surface. A point element A and a planar sur-face B are opposed if the following conditions apply: Vectors originating and extending from point A and surface B, that are coincident to a line through point A and normal to surface B, and directed away from the material, must be in opposite directions and normal to the surface from which the point element is derived. The

element and planar surface is opposed if a vec-tor originating and extending normal from sur-face B intersects point A. When the point ele-ment and planar surface lie in the same plane, they shall not be considered opposed elements. See Fig. 1-58(c).

1.3.41.4 Opposed Parallel Line Elements. Two (2) line elements, A and B, are opposed if the following conditions apply: Vectors originat-ing and extending normal from lines A and B in a plane containing lines A and B, and directed away from the material, must be in opposite directions and normal to the surfaces from which the line elements are derived. Two line ele-ments are opposed if a vector originating and extending normal from line element A intersects line element B. When both lines lie on the same planar surface, other than the surface edges, they shall not be considered opposed line ele-ments. See Figs. 1-58(d) and 1-66.

1.3.41.5 Opposed Parallel Line Element and Planar Surface. A line element A and a planar surface B are opposed if the following conditions apply: Vectors originating and extending normal from line A and planar surface B in a plane con-taining line A and normal to surface B, and di-rected away from the material, must be in oppo-site directions. Line element A and planar sur-face B are opposed if a vector originating and extending normal from line element A intersects planar surface B. If line element A lies on a planar surface perpendicular to surface B, other than the surface edge, they are not considered opposed elements. See Fig. 1-58(e).

1.3.41.6 Opposed Parallel Surfaces. Two (2) surfaces, A and B, are opposed if the following conditions apply: The two surfaces are planar. Vectors, originating and extending normal from surfaces A and B, and directed away from the material, must be in opposite directions. Two surfaces are opposed if a vector originating and extending normal from surface A intersects sur-face B. See Figs. 1-58(f) and 66.

1.3.42 Uniform Thickness/Gap. A condition where two surfaces are nominally equidistant.

1.3.43 Uniform Thickness/Gap Feature. A pair of continuous surfaces or portions thereof that are nominally equidistant and associated with a Uniform Thickness/Gap tolerance. The surface normal vectors directed away from each sur-face's material side must be in opposite direc-tions.



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Note: A Uniform Thickness/Gap Feature is not a feature of size.

1.3.44 Circular Element. The intersection of a surface of revolution and a planar section per-pendicular to the axis of the surface of revolution that nominally occupies more than 180 degrees of rotation around the axis.

1.3.45 Cylindrical Surface. A single surface of revolution at a constant nominal radius contain-ing at least one circular element that nominally occupies more than 180 degrees of rotation around an axis. (For Example. shaft, hole, pin, etc.)

1.3.46 Obstruction. A protrusion that violates a part surface and does not constitute an interrup-tion. See Fig. 1-68(b).

1.3.47 Recess. An opening that violates a part surface and does not constitute an interruption. See Fig. 1-68(a).

1.3.48 Interruption. A protrusion or opening that constitutes a complete break resulting in more than one distinct partial surface or ele-ment. (i.e., full length of a major diameter of an external spline shaft, annular groove(s), star pin, etc.).

1.3.49 Bounded Feature. The surface that results from a closed contiguous contour in a given plane projected along a vector normal to the plane. (For example: The material that re-mains or is removed by extruding an outline of a planar closed geometric shape in a single vector direction through material.) See Fig. 1-67(a).

1.3.50 Pattern. Two (2) or more features or features of size to which a locational geometric tolerance is applied and are grouped by one of the following methods (per Y14.5M-1994): nX, nCOAXIAL HOLES, ALL OVER, A ↔ B, nSUR-FACES, or INDICATEDα. 1.4 Fundamental Rules. Dimensioning and tolerancing shall clearly define engineering intent and shall conform to the following.

a) Each dimension shall have a tolerance, ex-cept for those dimensions specifically identified as reference, maximum, minimum, or stock (commercial stock size). The tolerance may be applied directly to the dimension (or indirectly in the case of basic dimensions), indicated by a general note, or located in a supplementary block of the drawing format. See ANSI Y14.1.

(b) Dimensioning and tolerancing shall be com-plete so there is full understanding of the charac-

teristics of each feature. Neither scaling (meas-uring the size of a feature directly from an engi-neering drawing) nor assumption of a distance or size is permitted, except as follows: Undimen-sioned drawings, such as loft, printed wiring, templates, and master layouts prepared on sta-ble material, are excluded provided the neces-sary control dimensions are specified.

(c) Each necessary dimension of an end product shall be shown. No more dimensions than those necessary for complete definition shall be given. The use of reference dimensions on a drawing should be minimized.

(d) Dimensions shall be selected and arranged to suit the function and mating relationship of a part and shall not be subject to more than one interpretation.

(e) The drawing should define a part without specifying manufacturing methods. Thus, only the diameter of a hole is given without indicating whether it is to be drilled, reamed, punched, or made by any other operation. However, in those instances where manufacturing, processing, quality assurance, or environmental information is essential to the definition of engineering re-quirements, it shall be specified on the drawing or in a document referenced on the drawing.

(f) It is permissible to identify as nonmandatory certain processing dimensions that provide for finish allowance, shrink allowance, and other requirements, provided the final dimensions are given on the drawing. Nonmandatory processing dimensions shall be identified by an appropriate note, such as NONMANDATORY (MFG DATA).

(g) Dimensions should be arranged to provide required information for optimum readability. Dimensions should be shown in true profile views and refer to visible outlines.

(h) Wires, cables, sheets, rods, and other mate-rials manufactured to gage or code numbers shall be specified by linear dimensions indicating the diameter or thickness. Gage or code num-bers may be shown in parentheses following the dimension.

(i) A 90 degree angle applies where center lines and lines depicting features are shown on a drawing at right angles and no angle is specified. See para. 2.1.1.2.

(j) A 90° basic angle applies where centerlines of features in a pattern or surfaces shown at right angles on the drawing are located or defined by basic dimensions and no angle is specified.



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(k) Unless otherwise specified, all dimensions are applicable at 20°C (68°F). Compensation may be made for measurements made at other temperatures.

(l) All dimensions and tolerances apply in a free state condition. This principle does not apply to nonrigid parts as defined in paras. 2.7.1.3(b) and 6.3.

(m) Unless otherwise specified, all geometric tolerances apply for full depth, length, and width of the feature.

(n) Dimensions and tolerances apply only at the drawing level where they are specified. A di-mension specified for a given feature on one level of drawing, (for example, a detail drawing) is not mandatory for that feature at any other level (for example, an assembly drawing).

(o) Unless otherwise specified all dimensions apply after heat treat and surface treatment.

(q) A zero basic dimension applies where axes, center planes or surfaces are shown congruent on a drawing.

(r) Direct tolerancing methods as described in paragraph 2.2 shall not be used to locate fea-tures or features of size. Angle tolerance as described in paragraph 2.2 shall not be used to orient features of size.

Note: Direct tolerancing methods may be used for Uniform thickness/gap, size and depth of counterbores, size and depth of countersinks, size and depth of spotfaces, size of chamfers, size of corner radii, thread depth, and surface intersections. The dimension origin symbol should be used when direct tolerancing is speci-fied for the examples noted. See Fig. 1-73.

1.5 Units of Measurement.

1.5.4 Angular Units. Angular dimensions are expressed in degrees and decimal parts of a degree. See Fig. 1-1.

Note: Toleranced angles using de-gree/minutes/seconds as shown in Fig’s 1-1, 2-1, 2-2, and 2-13 shall not be used. 1.7 Application Of Dimensions).

1.7.1 Dimension Lines. A dimension line, with its arrowheads, shows the direction and extent of a dimension. Numerals indicate the number of units of a measurement. Dimension lines shall be broken for the insertion of numerals as shown in Fig’s 1-2 and 1-4. . The following shall not be used as a dimension line: a center line, an ex-tension line, a phantom line, a line that is part of the outline of the object, or a continuation of any of these lines. A dimension line is not used as an extension line.

1.7.9 Dimensions Not to Scale. Paragraph 1.7.9(b) of ASME Y14.5 shall not be used. 1.8 Dimensioning Features.

1.8.13 Spotfaces. The diameter of the spot-faced area is specified. See Fig. 1-40. Either the depth or the remaining material shall be speci-fied. 1.9 Location Of Features.

1.9.5 Repetitive Features or Dimensions. Repetitive features or dimensions may be speci-fied by the use of an X in conjunction with a nu-meral to indicate the “number of places” re-quired. Where used with a basic dimension, the X shall be placed outside the basic dimension frame.



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Figure 1-57 – Related And Unrelated Actual Mating Envelope



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Figure 1-58 – Definition Of Opposed And Feature Of Size



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Figure 1-59 – Interrupted Cylindrical Feature Of Size



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Figure 1-60 Interrupted Opposed Parallel Surfaces Feature Of Size



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Figure 1-61 – Opposed Line Elements Feature of Size DATUM



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Figure 1-62 – Cylindrical Whole Feature Of Size



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Figure 1-63 – Cylindrical Whole Feature Of Size



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Figure 1-64 – Circular Element Interrupted Feature Of Size

Figure 1-65 – Circular Element Interrupted Feature Of Size



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Figure 1-66 – Features Of Size – Opposed Parallel Line Elements And Opposed Parallel Surfaces



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Figure 1-67 – Bounded Feature Of Size



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Figure 1-68 – Recess And Obstruction



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Figure 1-69 - Interrupted Feature



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Figure 1-70 - Whole Circular Element Feature Of Size



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Figure 1-71 Whole Feature Of Size



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Figure 1-72 - Whole Feature Of Size



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Figure 1-73 – Direct Tolerancing



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Figure 1-74 – Interrupted Opposed Parallel Surfaces Feature Of Size

2 General Tolerancing and Related Principles 2.7 Limits Of Size. The following paragraphs define the criteria for the specified limits of a fea-ture of size. These criteria apply solely to individ-ual features of size as defined in Para. 1.3.11 of this addendum.

2.7.1 Individual Feature of Size. The form of an individual feature of size is controlled to the extent prescribed in the following paragraphs. (a) Where only a tolerance of size is specified, (i.e., no geometric tolerance of form, orientation, or position is specified), the limits of size of the individual feature of size prescribe the extent to which variations in its geometric form, as well as size are allowed. Variation in form is allowed

provided the feature of size does not extend beyond a boundary of perfect form at MMC.

(b) Where a geometric tolerance is applied to a feature of size regardless of feature size, and no geometric form tolerance is specified, the limits of size of the individual feature of size prescribe the extent to which variations in its geometric form, as well as size, are allowed. Variation in form is allowed provided the feature of size does not extend beyond a boundary of perfect form at MMC. (c) Where a geometric tolerance of orientation is applied to a feature of size at maximum material condition and no geometric form tolerance is specified, variations in form are constrained by the MMC virtual condition of the specified orien-tation tolerance. Where only a geometric toler-ance of position is applied at maximum material condition, variations in form are constrained by the MMC virtual condition of the specified posi-



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tion tolerance. Variation in form is allowed pro-vided the feature of size does not extend beyond the MMC virtual condition of the applicable orien-tation or position tolerance. (d) Where a geometric tolerance of orientation is applied to a feature of size at least material con-dition and no geometric form tolerance is speci-fied, variations in form are constrained by the LMC virtual condition of the specified orientation tolerance. Where only a geometric tolerance of position is applied at least material condition, variations in form are constrained by the LMC virtual condition of the specified position toler-ance. Variation in form is allowed provided the feature of size does not extend beyond the LMC virtual condition of the applicable orientation or position tolerance.

2.7.1.1 Variations of Size. The actual local size of an individual whole feature of size at each cross section shall be within the specified toler-ance of size except where a feature of size is truncated or has an obstruction or recess.

Note: When a feature of size contains a trunca-tion, obstruction, recess or interruption, portions of the part surface have no opposing elements and the actual local size cannot be found. Where non-opposed elements exist in a feature of size, the size and form of the surface must be within the maximum and minimum boundaries established by paragraph 2.1.1.

2.7.1.2 Variations of Form (Envelope Princi-ple). Paragraph 2.7.1.2 of ASME Y14.5 shall not be used.

2.7.3 Relationship Between Individual Fea-tures. The limits of size do not control the ori-entation or location relationship between individ-ual features. Features shown perpendicular, coaxial, or symmetrical to each other must be controlled for location or orientation to avoid incomplete drawing requirements. These con-trols may be specified by one of the methods given in Sections 5 and 6. If it is necessary to establish a boundary of perfect form at MMC to control the relationship between features, the following methods are used.

(a) Specify a zero tolerance of orientation at MMC, including a datum reference (at MMC if applicable), to control angularity, perpendicular-ity, or parallelism of the feature. See para. 6.6.1.2.

(b) Specify a zero positional tolerance at MMC, including a datum reference (at MMC if applica-

ble) to control coaxial or symmetrical features. See paras. 5.11.1.3 and 5.13.2.



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2.8 Applicability of RFS, MMC, and LMC). Ap-plicability of RFS, MMC, and LMC is limited to features subject to variations in size. They may be datum features or other features whose axes or center planes are controlled by geometric toler-ances. In the case of straightness covered in paras. 6.4.1.1.2 and 6.4.1.1.3, it is the derived median line and the derived median plane, rather than the axis and center plane that are controlled. In all cases, the following practices apply for indi-cating RFS, MMC, and LMC:

(a) All Applicable Geometric Tolerances (Rule #2). RFS applies, with respect to the individual tolerance, datum reference, or both, where no modifying symbol is specified. MMC or LMC must be specified on the drawing where it is required.

Note: Circular runout and total runout, are appli-cable only on an RFS basis and cannot be modi-fied to MMC or LMC.

2.8.2 Effect of MMC. Where a geometric toler-ance is applied on an MMC basis, the allowable tolerance is dependent on the unrelated actual mating size of the considered feature of size. The tolerance is limited to the specified value if the feature of size is produced at MMC. Where the unrelated actual mating size of the feature of size has departed from MMC, an increase in the tolerance is allowed equal to the amount of such departure. The total permissible variation in the specific geometric characteristic is maximum when the unrelated actual mating envelope of the feature of size is equal to LMC value. Like-wise, referencing a datum feature of size on an MMC basis means the datum is the axis or cen-ter plane of the feature of size at the MMC limit or virtual condition. Where the unrelated actual mating size of a primary datum feature of size, or the related actual mating size of a secondary or tertiary datum feature of size has departed from MMC value, a deviation is allowed between its axis or center plane and the axis or center plane of the datum.

2.8.3 Effect of Zero Tolerance at MMC. Where a tolerance of position or orientation is applied on a zero tolerance at MMC basis, the tolerance is totally dependent on the unrelated actual mat-ing size of the considered feature. No tolerance of position or orientation is allowed if the feature is produced at its MMC limit of size. Where the unrelated actual mating size of the considered feature has departed from MMC, a tolerance is allowed equal to the amount of such departure. The total permissible variation in position or ori-

entation is maximum when the feature is at LMC, unless a maximum is specified. See Figs. 6-41 and 6-42.

2.8.4 Effect of LMC. Where a positional toler-ance is applied on an LMC basis, the allowable tolerance is dependent on the related actual mating size of the considered feature of size. The tolerance is limited to the specified value if the feature of size is produced at its LMC limit of size. Where the related actual mating size of the feature of size has departed from LMC, an in-crease in the tolerance is allowed equal to the amount of such departure. The total permissible variation in position is maximum when the fea-ture of size is at MMC. Likewise, referencing a datum feature of size on an LMC basis means the datum is the axis or center plane of the fea-ture of size at the LMC limit. Where the unre-lated actual mating size of a primary datum fea-ture of size, or the related actual mating size of a secondary or tertiary datum feature of size has departed from LMC, a deviation is allowed be-tween its axis or center plane and the axis or center plane of the datum.

2.8.5 Effect of Zero Tolerance at LMC. Where a tolerance of position or orientation is applied on a zero tolerance at LMC basis, the tolerance is totally dependent on the size of the considered feature. No tolerance of position or orientation is allowed if the feature is produced at its LMC limit of size where the unrelated actual mating size of the considered feature has departed from LMC, a tolerance is allowed equal to the amount of such departure. The total permissible variation in position or orientation is maximum when the feature is at MMC unless a maximum is speci-fied. See Figs. 5-13, 5-14, and 6-42.



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2.15 Radius.

2.15.2 Controlled Radius Tolerance. A con-trolled radius symbol CR creates a tolerance zone defined by two arcs (the minimum and maximum radii) that are tangent to the adjacent surfaces. When specifying a controlled radius, the part contour within the crescent-shaped tol-erance zone must be a fair curve without rever-sals. Additionally, radii taken at all points on the part contour shall neither be smaller than the specified minimum limit nor larger than the maximum limit. See Fig. 2-19. If a controlled radius is specified, the surface finish require-ments of the applicable radius must be noted. 2.16 Statistical Tolerancing. Statistical toleranc-ing as described in Para. 2.16 and associated sub-paragraphs of ASME Y14.5 shall not be used. 2.17 Uniform Thickness/Gap Tolerance. A Uni-form Thickness/Gap tolerance specifies that the minimum and maximum actual Thickness/Gap value, as defined in (a) and (b) below, must be

within the specified Uniform Thickness/Gap toler-ance limits.

(a) For a uniform thickness feature (external), the maximum actual thickness value is the mini-mum separation between two points a fixed dis-tance apart that the entire uniform thickness feature will pass through. The minimum actual thickness value is the minimum distance be-tween the surfaces of a uniform thickness fea-ture. See Fig. 2-24, 2-25 and 2-26. (b) For a uniform gap feature (internal), the minimum actual gap value is the maximum separation between two points a fixed distance apart that the entire uniform gap feature will pass over. The maximum actual gap value is the maximum distance between the surfaces of a uniform gap feature. See Fig. 2-23.



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Figure 2-23 – Uniform Gap Tolerancing – Internal Feature



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Figure 2-24 – Uniform Thickness Tolerancing – External Feature

Figure 2-25 – Uniform Thickness Tolerancing – Cylindrical Feature Of Size



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Figure 2-26 – Uniform Thickness Tolerancing – Formed Sheet Stock Part

3 Symbology 3.3 Symbol Construction.

3.3.2 Datum Feature Symbol. The symbolic means of indicating a datum feature consists of a capital letter enclosed in a square frame and a leader line extending from the frame to the con-cerned feature, terminating with a triangle. The triangle may be filled or not filled. See Fig. 3-2. Letters of the alphabet (except I, O, and Q) are used as datum identifying letters. Each datum feature of a part requiring identification shall be assigned a different letter. When datum fea-tures requiring identification on a drawing are so numerous as to exhaust the single alpha series, the double alpha series (AA through AZ, BA through BZ, etc.) shall be used and enclosed in a rectangular frame. Where the same datum feature symbol is repeated to identify the same feature in other locations of a drawing, it need not be identified as reference. The datum fea-ture symbol is applied to the concerned feature surface outline, extension line, dimension line, or feature control frame as follows:

(a) Placed on the outline of a feature surface, or on an extension line of the feature outline, clearly

separated from the dimension line, or placed above or below and attached to a feature control frame controlling the feature, when the datum feature is the surface itself. See Figs. 3-3 and 3-27.

(b) placed on an extension of the dimension line of a feature of size when the datum is the axis or center plane. If there is insufficient space for the two arrows, one of them may be replaced by the datum feature triangle. See Figs. 3-4(a) through (c).

(c) placed on the outline of a cylindrical feature surface or an extension line of the feature out-line, separated from the size dimension, when the datum is the axis. For CAD systems, The triangle may be tangent to the feature. See Figs. 3-4(d) and (f).

(d) placed on a leader line to the feature. See Fig. 4-40.

(e) placed on the planes established by datum targets on complex or irregular datum features (see para. 4.6.7), or to re-identify previously established datum axes or planes on repeated or multi-sheet drawing requirements.



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(f) placed above or below and attached to the feature control frame when the feature (or group of features) controlled is the datum axis or da-tum center plane. See Figs. 3-5 and 3-23.

(g) placed on an extension line parallel to the center plane and separated from the size dimen-sion, when only one plane of a cylindrical feature of size is the desired datum. See Fig. 3-28 for RFS application and Fig. 3-29 for MMC applica-tion.

(h) the use of a dashed radial leader line, as in Fig. 4-48 indicates that the datum feature is on the far (hidden) surface.

3.3.18 All Around Symbol. The symbolic means of indicating that a tolerance applies to surfaces all around the part is a circle located at the junction of the leader from the feature control frame. All around the part means all around the outline, only in the view in which the symbol is pointing to the outline. See Fig. 3-17.

3.3.24 Unequal Bilateral Symbol. The sym-bolic means of indicating that a tolerance applies either unilaterally or unequally disposed about the true profile. This symbol is used with Profile of a Line or Profile of a Surface. See Figs. 3-30 and 6-55.

3.3.25 Uniform Thickness/Gap Symbols. The symbolic means of indicating that a uniform Thickness/Gap tolerance applies. For a thick-ness feature (external), the notation THK follows a direct tolerance specification. See Fig. 2-24, 2-25 and Fig. 2-26. For a gap feature (internal), the notation GAP follows a direct tolerance specification. See Fig. 2-23.

3.5 Feature Control Frame Placement. The feature control frame is related to the considered feature by one of the following methods:

(a) locating the frame below or attached to a leader-directed callout or dimension pertaining to the feature. See Fig. 3-25.

(b) running a leader from the frame to the fea-ture; See Fig. 3-25.

(c) attaching a side or an end of the frame to an extension line from the feature, provided it is a plane surface; See Fig. 3-25.

(d) attaching a side or an end of the frame to an extension of the dimension line pertaining to a feature of size. See Fig. 3-25.

(e) locating the frame in a note or in a chart that clearly identifies the feature(s) to which the frame applies.



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Figure 3-27 – Datum Feature Symbol Placement – Surface

Figure 3-28 Datum Feature Placement – Feature Of Size – Rfs – One Direction



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Figure 3-29 – Datum Feature Placement – Feature Of Size – MMC – One Direction

Figure 3-30 – Size And Proportion Of Unequal Bilateral Symbol



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4 Datum Referencing 4.2 Immobilization Of Part. Where features of a part have been identified as datum features, the part is oriented and immobilized relative to the three mutually perpendicular planes of the datum reference frame in a selected order of prece-dence. This in turn makes the geometric relation-ships that exist between the features measurable. A true geometric counterpart of a feature used to establish a datum may be: (a) a plane; (b) a maximum material condition boundary (MMC concept); (c) a least material condition boundary (LMC con-cept); (d) a virtual condition boundary; (e) An unrelated actual mating envelope for a primary datum, or a related actual mating enve-lope for a secondary or tertiary datum; (f) a mathematically defined contour. 4.3 Datum Features.

4.3.1 Temporary and Permanent Datum. Fea-tures. Selected datum features of in-process parts, such as castings, forgings, machinings, or fabrications, may be used temporarily to estab-lish permanent datum features. It is recom-mended that such temporary datum features not be subsequently removed by manufacturing processes. 4.4 Specifying Datum Features In An Order Of Precedence. Datum features must be specified in an order of precedence to position a part properly on the datum reference frame. Figure 4-2 illus-trates a part where the datum features are plane surfaces. The desired order of precedence is indicated by entering the appropriate datum fea-ture reference letters, from left to right, in the fea-ture control frame. In fig. 4-2(a), the datum fea-tures are identified as Surfaces D, E, and F. These surfaces are most important to the design and function of the part, as illustrated by Fig. 4-2(b). Surfaces D, E, and F are the primary, sec-ondary, and tertiary datum features, respectively, since they appear in that order in the feature con-trol frame.

4.4.2 Parts With Cylindrical Datum Features. A cylindrical datum feature is associated with two theoretical planes of a datum reference frame intersecting at right angles on the datum axis when the cylindrical datum is primary; or secon-dary while the primary datum is a plane perpen-dicular to the cylindrical datum . The datum of a cylindrical surface is the axis of the true geomet-

ric counterpart of the datum feature (For exam-ple, unrelated actual mating envelope for RFS primary applications or related actual mating envelope for RFS secondary or tertiary applica-tions), and simulated by the axis of a cylinder in the processing equipment. The axis of the true geometric counterpart serves as the origin of measurement from which other features of the part are located. See Figs. 4-5, 4-11, and 4-12. 4.5 Establishing Datums.

4.5.1 Datum Features Not Subject to Size Variations. Where a nominally flat surface is specified as a datum feature, the corresponding datum is simulated by a plane contacting points of that surface. See Fig. 4-10. The extent of contact depends on whether the surface is a primary, a secondary, or a tertiary datum feature. See para. 4.4. If irregularities on the surface of a primary or secondary datum feature are such that the part is unstable (that is, it wobbles) when brought into contact with the corresponding sur-face of a fixture, the part may be adjusted to an optimum position, if necessary, to simulate the datum. See para. 4.3.3

(a) Datum feature – non-opposed to a datum axis. Where a feature is referenced as a secon-dary (or tertiary) datum and is non-opposed (off-set) to the datum axis (or center plane), the da-tum feature simulator is constrained by the basic dimensions of the drawing. See Fig. 4-40(a).

(b) Datum feature – opposed to a datum axis. Where a feature is referenced as a secondary (or tertiary) datum and is opposed to the datum axis (or center plane), the datum feature simula-tor is oriented relative to the higher ranking da-tums and is movable to accommodate allowable variation in the location of the datum feature. See Fig. 4-40(b).

4.5.3 Specifying Datum Features RFS. Where a datum feature of size is applied on an RFS basis, the datum is established by physical con-tact between the feature surface(s) and sur-face(s) of the processing equipment. A machine element that is variable in size (such as a chuck, mandrel, vise, or centering device) is used to simulate a true geometric counterpart of the feature and to establish the datum axis or center plane.

(a) Primary Datum Feature — Diameter RFS. The simulated datum is the axis of the true geo-metric counterpart of the datum feature. The true geometric counterpart (or unrelated actual mating envelope) is the smallest circumscribed (for an external feature) or largest inscribed (for



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an internal feature) perfect cylinder that contacts the datum feature surface. See Figs. 4-11 and 4-12.

(b) Primary Datum Feature — Width RFS. The simulated datum is the center plane of the true geometric counterpart of the datum feature. The true geometric counterpart (or unrelated actual mating envelope) is two parallel planes at mini-mum separation (for an external feature) or maximum separation (for an internal feature) that contact the corresponding surfaces of the datum feature. See Figs. 4-13 and 4-14.

(c) Secondary Datum Feature RFS — Diameter or Width. For both external and internal fea-tures, the secondary datum (axis or center plane) is established in the same manner as indicated in (a) and (b) above with an additional requirement: The contacting cylinder or parallel planes of the true geometric counterpart must be oriented to the primary datum (usually a plane) — that is, the related actual mating envelope relative to the primary datum. Datum B in Fig. 4-15 illustrates this principle for diameters; the same principle applies for widths.

(d) Tertiary Datum Feature — Diameter or Width RFS. For both external and internal features, the tertiary datum (axis or center plane) is estab-lished in the same manner as indicated in (c) above with an additional requirement: The con-tacting cylinder or parallel planes must be ori-ented in relation to both the primary and the secondary datum — that is, the related actual mating envelope relative to the primary and sec-ondary datum. The tertiary datum feature may be aligned with a datum axis as in Fig. 4-15 or offset from a plane of the datum reference frame.

(e) Datum feature of size (RFS) – non-opposed to a datum axis. Where a feature of size is ref-erenced at RFS as a secondary (or tertiary) da-tum and is not opposed to the datum axis or center plane, the true geometric counterpart is constrained by the basic dimension. See Fig. 4-41(a). (f) Datum feature of size (RFS) – opposed to a datum axis. Where a feature of size is refer-enced at RFS as a secondary (or tertiary) datum and is opposed to the datum axis or center plane, the true geometric counterpart is oriented relative to the higher ranking datums and is movable to accommodate allowable variation in the location of the feature of size. See Fig. 4-41(b).

4.5.4 Specifying Datum Features at MMC. Where a datum feature of size is applied on an MMC basis, machine and gaging elements in the processing equipment that remain constant in size may be used to simulate a true geometric counterpart of the feature and to establish the datum. In each case, the size of the true geo-metric counterpart is determined by the specified MMC limit of size of the datum feature, or its MMC virtual condition, where applicable.

(a) Datum feature of size (MMC) – non-opposed to a datum axis. Where a feature of size is ref-erenced at MMC as a secondary (or tertiary) datum and is not opposed to the datum axis or center plane, the true geometric counterpart is constrained by the basic dimension. See Fig. 4-42(a).

(b) Datum feature of size (MMC) – opposed to a datum axis. Where a feature of size is refer-enced at MMC as a secondary (or tertiary) da-tum and is opposed to the datum axis or center plane, the true geometric counterpart is con-strained by the basic dimensions. See Fig. 4-42(b).

4.5.5 Specifying Datum Features at LMC. The method in paragraph 4.5.5 of ASME Y14.5 shall not be used.

4.5.6.2 Surface Primary. In Fig. 4-18(c), sur-face B is the primary datum feature; diameter A is the secondary datum feature and RFS is ap-plied. The datum axis is the axis of the smallest circumscribed cylinder that contacts diameter A and is perpendicular to the datum plane — that is, the related actual mating envelope of a di-ameter that is perpendicular to datum plane B. In addition to size variations, this cylinder encom-passes any variation in perpendicularity between diameter A and surface B, the primary datum feature.

4.5.6.3 Cylindrical Feature at MMC Secon-dary. In Fig. 4-18(d), surface B is the primary datum feature; diameter A is the secondary da-tum feature and MMC is applied. The datum axis is the axis of a virtual condition cylinder of fixed size that is perpendicular to the datum plane B. Variations in the size and perpendicu-larity of datum feature A are permitted to occur within this cylindrical boundary. Furthermore, as the related actual mating envelope of datum feature A departs from its maximum size, a dis-placement of its axis relative to the datum axis is allowed. See para. 5.1.2.



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4.5.7.1 Simulation of a Single Datum Plane. Fig. 4-20 and Fig. 4-43 are examples of a single datum plane simulated, by simultaneously con-tacting the high points of two surfaces. Identifi-cation of two features to establish a single datum plane may be required where separation of the features is caused by an obstruction, such as in Fig. 4-20, or by a recess (for example, a slot) of sufficient width. For controlling co-planarity of these surfaces, see Para. 6.5.6.

4.5.7.3 Specifying a Plane And a Feature of Size as a Single Datum Reference. Where it is desired to use a surface and a feature of size as a single datum reference, the method shown in Fig. 4-46 may be used.

4.5.13 Specifying Parallel Offset Datum Fea-tures. Where it is desired to use parallel offset planar features to establish a datum, the method shown in Fig. 4-44 may be used.

4.5.14 Specifying Angled Datum Features Simultaneously. Where it is desired to use two angled features to establish a single datum, the method shown in Fig. 4-45 may be used. 4.6 Datum Targets.

4.6.1.3 Datum Target Areas. The datum target area may be indicated by section lines inside a phantom outline of the desired shape, with con-trolling basic dimensions added. The diameter of circular areas is given in the upper half of the datum target symbol. See Figs. 4-29(a) and 4-51. Where it becomes impracticable to delineate a circular target area, the method of indication shown in Fig. 4-29(b) may be used.

4.6.2 Datum Target Dimensions. When di-mensions are used to define the location of da-tum targets, they shall be defined with basic dimensions. Basic dimensions are omitted when the true geometric counterpart of datum targets are movable. When the true geometric counter-part of a datum target is movable, a note de-scribing the movement of the targets shall be specified. See Fig. 4-51.

4.6.7 Datums Established from Datum Tar-gets. The datum feature symbol shall be at-tached only to identifiable datum features. Where datums are established by the true geo-metric counterpart of datum targets, the datum planes may be identified as shown in Fig. 4-51. 4.7 Restraining Datum Features. It may be de-sirable during dimensional measurement to re-strain a part or assembly to simulate its function or interaction with other parts or assemblies. In

these cases, geometric tolerances apply with the specified datum feature(s) referenced in feature control frame(s) restrained to the nominally de-signed condition. This section establishes the principles and methods for defining and referenc-ing restrained datum features.

4.7.2 Specifying The Restrained Requirement As Default. MAKE BOLDTo invoke the re-strained requirement, a note similar to the ones shown in Figs. 4-47 and 4-48, shall be shown on the drawing.

4.7.4 Specifying The Unrestrained Require-ment For A Particular Datum(s) When The Restrained Condition Is Noted. Where an individual orientation or location tolerance is applied to a feature and the default restrained requirement is noted, the free state symbol may be used to indicate that the restrained require-ment does not apply to particular datum fea-tures. The free state symbol is specified follow-ing the datum reference and any modifiers in the feature control frame. The part may or may not contact the unclamped datum target simulator when the datum targets define the datum plane. The part surface in the area of the unrestrained datum target shall be within the tolerance speci-fied for that surface. See Figs. 4-47 and 4-49.

4.7.5 Restraining Parts Using Features Of Size. It may be necessary to use multiple fea-tures of size to establish datum planes when the restrained requirement is invoked. In order for the datum features to engage the datum feature simulators, forces may be applied in accordance with the specified restraint requirement to flex or deform the part. See Fig. 4-50.

Note: The position tolerance shown in Fig. 4-50 for datum feature B (pattern of four holes) is not used to measure the free state location of the holes. It is used to establish the virtual condition pins that will restrain the part in an installed con-dition.

4.7.7 Contacting Datum Simulators. When restraint is applied, all datum features shall con-tact all datum feature simulators, unless other-wise specified. Full contact of the entire datum feature with the datum feature simulators not required, unless otherwise specified.

4.7.8 Use Of Material Condition Modifiers with Restrained Datums. When using features of size as datum features, consideration must be given to the material condition (MMC or RFS) at which the datum features apply. When the fea-ture control frame specifies a secondary or terti-

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ary datum feature of size is to apply RFS, the part is placed on the primary datum surface or datum targets, positively positioned on the RFS datum features of size and then clamped. In the case of secondary or tertiary datum features of size specified to apply at MMC, the part may be moved on the gage within the allowable gage looseness (difference between the virtual condi-tion boundary and the actual mating size) to optimize the part location and then clamped.

4.7.9 Pattern of Features as A Secondary or Tertiary Datum Feature. When applying GD&T to some types of parts, such as flexible plastics, i.e., fascias, shields, or covers, it may be neces-sary to utilize a pattern of features to establish a secondary (ASME Y14.5M-1994 Para. 4.5.8) or tertiary plane when the restrained requirement is invoked. In Fig. 4-48 the primary datum estab-lishes the part in the Z (height) plane, datum feature B establishes the X (length) and Y (width) planes. Because the part is not rigid, it is necessary to provide additional datum features in the X (length) direction. Two slots, which are both called datum feature C are used for this additional support. See Fig. 4-48. 4.8 Restraining Conditions. Several considera-tions must be made relative to restraining a part to verify tolerances.

4.8.1 Application Of Force On A Restrained Datum. The amount of force used to restrain a part shall be one of the following:

(a) the amount required RESTRAINING the part on the datum feature simulators compliant to para 4.7.7.

(b) The amount of force specified is equal to the force the part will be subjected to in its installed condition. In such cases, the range of accept-

able force (clamp load, torque, etc.) shall be specified. When this method is used, the re-straining force shall be shown on the drawing or specified in another document. If the force is specified in another document, the document shall be noted on the product drawing. See ASME Y14.5M Fig. 6-54.

4.8.2 Location, Direction and Size of Re-straint on A Restrained Datum Feature. The location, direction and size of restraint shall be shown on the drawing or specified in another document. If the location, direction and size of restraint is specified in another document, the document shall be noted on the product drawing. Additional restraints may not be used unless specifically designated on the drawing.

(a) When datum targets are specified, the loca-tion and direction is applied over each datum target, normal to the datum and the same size and shape of the datum target unless otherwise specified.

(b) When the entire surface is specified as the datum feature, the location and direction is ap-plied over the datum feature, normal to the da-tum and the same size and shape of the datum feature unless otherwise specified.

4.8.3 Sequence Of Restraints On A Re-strained Datum Reference Frame. The se-quence of applying restraints shall be specified in the following manner:

(a) On the drawing with a note.

(b) Described in another document, with refer-ence to the other document on the drawing.



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Figure 4-40 – Interpretation For Secondary (Or Tertiary) Datum Feature Where Next Higher Ranking Datum Is An Axis (Or Center Plane) – Secondary (Or Tertiary) Datum Feature Is A Plane



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Figure 4-41 – Interpretation For Secondary (Or Tertiary) Datum Feature Where Next Higher Ranking Datum Is An Axis (Or Center Plane) – Secondary (Or Tertiary) Datum Feature Is A Feature Of Size –

RFS



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Figure 4-42 – Interpretation For Secondary (Or Tertiary) Datum Feature Where Next Higher Ranking Datum Is An Axis (Or Center Plane) – Secondary (Or Tertiary) Datum Feature Is A Feature Of Size –

MMC



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Figure 4-43 – Method Of Specifying Coplanar Datum Features – Common Plane

Figure 4-44 – Method Of Specifying Coplanar Datum Features – Parallel Offset Planes



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Figure 4-45 – Using Angled Part Features As Datum Features



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Figure 4-46 – Surface And Feature Of Size At MMC, Single Datum Reference



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Figure 4-47 – Indication Of Unrestrained Datum Targets



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Figure 4-48 – Multiple Features Of Size As A Secondary Or Tertiary Datum Feature



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Figure 4-49 – Specifying Restrained Datum



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Figure 4-50 – Part Restrained On Features Of Size



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Figure 4-51 – Datum Target Areas

5 Tolerances of Location 5.3 Fundamental Explanation of Positional Tolerancing.

5.3.2.1 Explanation of Positional Tolerance at MMC. A positional tolerance applied at MMC may be explained in either of the following ways.

(a) In Terms of the Surface of a Hole. While maintaining the specified size limits of the hole, no element of the hole surface shall be inside a theoretical boundary located at true position. See Fig. 5-5.

(b) In Terms of the Axis of a Hole. Where a hole is at MMC (minimum diameter), its axis must fall within a cylindrical tolerance zone whose axis is located at true position. The diameter of this zone is equal to the positional tolerance. See Figs. 5-6(a) and (b). This tolerance zone also defines the limits of variation in the orientation of the axis of the hole in relation to the datum sur-face. See Fig. 5-6(c). It is only where the hole is at MMC that the specified tolerance zone ap-plies. Where the unrelated actual mating size of the hole is larger than MMC, additional positional

tolerance results. See Fig. 5-7. This increase of positional tolerance is equal to the difference between the specified maximum material condi-tion limit of size (MMC) and the unrelated actual mating size of the hole. Where the unrelated actual mating size is larger than MMC, the speci-fied positional tolerance for a hole may be ex-ceeded and still satisfy function and inter-changeability requirements.

Note: In certain cases of extreme form deviation (within limits of size) or orientation deviation of the hole, the tolerance in terms of the axis may not be exactly equivalent to the tolerance in terms of the surface. In such cases, the surface interpretation shall take precedence.

5.3.2.2 Displacement Allowed by Datum Fea-tures at MMC. In many instances, a group of features (such as a group of mounting holes) must be positioned relative to a datum feature at MMC. See Fig. 5-8. Where datum feature B is at MMC, its axis determines the location of the pattern of features as a group. Where datum feature B departs from MMC, its axis may be displaced relative to the location of the datum axis (datum B at MMC) in an amount equal to



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one-half the difference between its actual mating size and MMC size. Note: If a functional gage is used to check the part, the shift of the axis of the datum feature is automatically accommodated. However, if open set-up inspection methods are used to check the location of the feature pattern relative to the axis of the datum feature’s actual mating envelope, this must be taken into account. Since the axis of the datum features actual mating envelope must serve as the origin of measurements for the pattern of features, the features are therefore viewed as if they, as a group, had been displaced relative to the axis of the datum feature’s actual mating envelope. This relative shift of the pattern of features, as a group, with respect to the axis of the datum feature does not effect the positional tolerance of the features relative to one another within the pattern. Note: The actual mating envelope would be unrelated for a primary datum feature and re-lated for a secondary or tertiary datum feature.

5.3.3 Zero Positional Tolerance at MMC. In the preceding explanation, a positional tolerance of some magnitude is specified for the location of features. The application of MMC permits the tolerance to exceed the value specified, provided features are within size limits, and the feature locations are such as to make the part accept-able. However, rejection of usable parts can occur where these features are actually located on or close to their true positions, but produced to a size smaller than the specified minimum (outside of limits). The principle of positional tolerancing at MMC can be extended in applica-tions where it is necessary to provide greater tolerance within functional limits than would oth-erwise be allowed. This is accomplished by adjusting the minimum size limit of a hole to the absolute minimum required for insertion of an applicable fastener located precisely at true posi-tion, and specifying a zero positional tolerance at MMC. In this case, the positional tolerance al-lowed is totally dependent on the unrelated ac-tual mating size of the considered feature, as explained in para. 2.8.3.

5.3.3.1 Example of Zero Positional Tolerance at MMC. Figure 5-10 shows a drawing of the same part with a zero positional tolerance at MMC specified. Note that the maximum size limit of the clearance holes remains the same, but the minimum was adjusted to correspond with a 14 mm diameter fastener. This results in an increase in the size tolerance for the clear-

ance holes, the increase being equal to the con-ventional positional tolerance specified in Fig. 5-9. Although the positional tolerance specified in Fig. 5-10 is zero at MMC, the positional toler-ance allowed is in direct proportion to the actual clearance hole size as shown by the following tabulation:

Clearance Hole Diameter

(Feature Unrelated Actual Mating Size)

Positional Tolerance Diameter Allowed

14 0

14.1 0.1

14.2 0.2

14.25 0.25

14.3 0.3

14.4 0.4

14.5 0.5

5.3.4 RFS as Related to Positional Toleranc-ing. In certain cases, the design or function of a part may require the positional tolerance, datum reference, or both, to be maintained regardless of the features’ unrelated actual mating sizes. RFS, where applied to the positional tolerance of circular features, requires the axis of each fea-ture to be located within the specified positional tolerance regardless of the size of the feature. This requirement imposes a closer control of the features involved and introduces complexities in verification. 5.11 Coaxiality Controls.

5.11.1.7 Coaxial Relationships Using Posi-tional Tolerance Without a Datum Reference. Where a part has two or more coaxial diameters, and only the interrelationship between the fea-tures of size is controlled with position tolerance, no datum references are specified. If the posi-tion tolerance is applied RFS, the axes of the unrelated actual mating envelopes must be within the specified cylindrical tolerance zone simultaneously. If the position tolerance is ap-plied MMC, the feature surfaces must be within the coaxial virtual conditions simultaneously. See Figs. 5-63 and 5-64.

5.11.1.8 Symmetrical Relationships Using Positional Tolerance Without a Datum Refer-ence. Where a part has two or more coaxial diameters, and only the interrelationship be-tween the features of size is controlled with posi-tion tolerance, no datum references are speci-fied. If the position tolerance is applied RFS, the



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axes of the unrelated actual mating envelopes must be within the specified cylindrical tolerance zone simultaneously. If the position tolerance is applied MMC, the feature surfaces must be within the coaxial virtual conditions simultane-ously. 5.12 Concentricity.

5.12.1 Concentricity Tolerancing. Paragraph 5.12.1 of ASME Y14.5 shall not be use.

5.12.2 Difference Between Coaxiality Con-trols and Concentricity. Paragraph 5.12.2 of ASME Y14.5 shall not be used. 5.13 Positional Tolerancing For Symmetrical Relationships. Positional tolerancing for symmet-rical relationships is that condition where the cen-ter plane of the unrelated actual mating envelope of one or more features is congruent with axis or center plane of a datum feature within specified limits. MMC, IMC, or RFS modifiers may be specified to apply to both the tolerance and the datum feature.

5.14 Symmetry Tolerancing to Control the Median Points of Opposed or Correspond-ingly Located Elements of Features. Paragraph 5.14 of ASME Y14.5 shall not be used. 5.16 Position Of A Cylindrical Part With Bends. To constrain the boundary of a nominally cylindri-cal part with bends, such as a tube, hose or rod, the position symbol is used in the feature control frame with the between symbol specified beneath. An MMC modifier must be specified in the toler-ance portion of the feature control frame. The collective effects of the MMC condition of the stated size tolerance and the associated position tolerance define the boundary. The tolerance applies to the extent defined by the between specification including the bend areas. When datums are not specified, the tolerance specifica-tion controls the form and the interrelationship between the applicable features. When datums are specified, the form is constrained by the boundary established by the position or orientation control. See Fig. 5-65.



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Figure 5-63 – Coaxial Features Of Size – Same Size – Without Datum Reference

Figure 5-64 – Coaxial Features Of Size – Different Sizes – Without Datum Reference



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Figure 5-65 – Position Tolerancing Of A Nominally Cylindrical Feature Of Size With Bends

6 Tolerances of Form, Profile, Orien-tation, and Runout 6.5 Profile Control.

6.5.1 Profile Tolerancing. The profile tolerance specifies a uniform boundary along the true pro-file within which the elements of the surface must lie. It is used to control form or combina-tions of size, form, orientation, and location. Where used as a refinement of size, the profile tolerance must be contained within the size lim-its. Profile tolerances are specified as follows.

(a) An appropriate view or section is drawn showing the desired basic profile.

(b) Unilaterally and unequally disposed profiles may be specified in a feature control frame with a leader directed to the surface. When specify-ing a profile of a surface tolerance unilaterally or unequal disposed bilaterally, the Unequal Bilat-eral symbol is added to the feature control frame following the tolerance value. A second value is added following the Unequal Bilateral symbol to indicate the amount of the tolerance that applies outside of the material. See Figs. 3-30 and 6-55. (In the following figures of Y14.5 the method of specifying unilateral or unequal bilateral profile tolerancing is replaced by the method described in this addendum: Figs: 6-11, 6-15, 6-16, 6-18.)



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(c) Where a profile tolerance applies all around the profile of a part, the symbol used to desig-nate “all around” is placed on the leader from the feature control frame. See Fig. 6-12. Where segments of a profile have different tolerances, the extent of each profile tolerance may be indi-cated by the use of reference letters to identify the extremities or limits of each requirement. See Fig. 6-13. Similarly, if some segments of the profile are controlled by a profile tolerance and other segments by individually toleranced dimensions, the extent of the profile tolerance must be indicated. See Fig. 6-14.

6.5.5.1 Boundary Control for a Noncylindrical Feature. Profile tolerancing may be combined with positional tolerancing where it is necessary to control the boundary of a noncylindrical fea-ture. See Fig 6-56. In this example, the basic dimensions and the profile tolerance establish a tolerance zone to control the shape and size of the feature. Additionally, the positional tolerance establishes a theoretical boundary shaped iden-tically to the basic profile. For an internal fea-ture, the boundary equals the MMC size of the profile minus the positional tolerance, and the entire feature surface must lie outside the boundary. For an external feature, the boundary equals the MMC size of the profile plus the posi-tional tolerance, and the entire feature surface must lie within the boundary. To invoke this concept, the term BOUNDARY is placed be-neath the positional tolerance feature control frame. Geometric tolerances applied as a boundary control for a noncylindrical feature (i.e., position or orientation controls) may be specified with a single leader line as shown in Fig. 6-56.

6.5.9.1.1 Explanation of Composite Control. Each feature is located from specified datums by basic dimensions. Datum referencing in the upper segment of a composite profile feature control frame serves to locate the feature profile locating tolerance zone relative to specified da-tums. See Figs. 6-25 and 6-26. The lower seg-ment serves to establish the limits of form and/or size. When datums are specified in the lower segment, the tolerance zone is oriented to the datums. See Figs. 6-25 and 6-26. The tolerance values represent the distance between two boundaries disposed about the true profile as defined by the basic dimensions and respective applicable datums. The actual surface of the controlled feature must lie within both the profile locating tolerance zone and the profile size/form/orientation tolerance zone.

6.6 Orientation Tolerances. 6.6.2 Angularity. Angularity is the condition of a surface, center plane, or axis at a specified angle from a datum plane or axis.

6.6.2.1 Angularity Tolerance. An angularity tolerance specifies one of the following:

(a) a tolerance zone defined by two parallel planes at the specified basic angle from one or more datum planes or a datum axis, within, which the surface or center plane of the consid-ered feature must lie. See Fig. 6-27.

(b) a tolerance zone defined by two parallel planes at the specified basic angle from one or more datum planes or a datum axis, within, which the axis of the considered feature must lie. See Fig. 6-28.

(c) A cylindrical tolerance zone at the specified basic angle from one or two datum planes, or a datum axis within which the axis of the consid-ered feature of size must lie. See Fig. 6-29

(d) a tolerance zone defined by two parallel lines at the specified basic angle from a datum plane or axis, within, which the line element of the sur-face must lie.

6.8 Free State Variation.

6.8.1 Specifying Geometric Tolerances on Features Subject to Free State Variation. Where tolerance is applied to a feature in the free state, specify the maximum allowable free state variation with an appropriate feature control frame. See Fig. 6-53. The free state symbol may be placed within the feature control frame, following the tolerance and any modifiers, to clarify a free state requirement on a drawing containing restrained feature notes, or to sepa-rate a free state requirement from associated features having restrained requirements. See Figs. 3-18 and 6-54.

6.8.2 Specifying Geometric Tolerances on Features to Be Restrained When a general restraint note is specified on the drawing, all geometric tolerances shall be within stated val-ues unless otherwise specified.



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Figure 6-55 – Specifying Unequal Profile Tolerance



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Figure 6-56 – Boundary Principle With Unequal Profile Tolerance



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Appendix B – Formulas For Posi-tional Tolerancing B1 General

The purpose of this Appendix is to present for-mulas for determining the required positional tolerances or the required sizes of mating fea-tures to ensure that parts will assemble. The formulas are valid for all types of features or patterns of features and will give a “no interfer-ence, no clearance” fit when features are at maximum material condition with their locations in the extreme of positional tolerance. Consid-eration must be given for additional geometric conditions that could affect functions not ac-counted for in the following formulas. When calculating positional tolerancing, conditions such as fastener straightness, thread to shank run out, and projected fastener length, need to be considered to ensure assembly.



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Appendix New F – Effect Of Changes To The Definition Of Actual Mating Envelope On The Figures In Y14.5. F1 General Fig. 4-11 change (smallest circumscribed cylin-der) to (unrelated actual mating envelope).

Fig. 4-12 change (Largest inscribed cylinder) to (Unrelated actual mating envelope).

Fig. 4-13 change (Parallel planes at minimum separation) to (Unrelated actual mating envelope).

Fig. 4-14 change (Parallel planes at maximum separation) to (Unrelated actual mating envelope).

Fig. 4-15 change (Parallel planes at maximum separation perpendicular to datum plane A. Center plane aligned with datum axis B.) To (Related actual mating envelope perpendicular to datum plane A. Center plane aligned with datum axis B.)

Fig. 4-18(b) change (Smallest circumscribed cylinder) to (Unrelated actual mating envelope).

Fig. 4-18(c) change (Smallest circumscribed cylinder perpendicular to datum plane B) to (Related actual mating envelope perpendicular to datum plane B).

Fig. 4-21 change smallest pair of coaxial circumscribed cylinders to Related actual mating envelope (Smallest pair of coaxial circumscribed cylinders).

Fig. 5-56 change "Axis of actual mating envelope" to "Axis of related actual mating envelope".

Fig. 5-57 change "Axis of actual mating envelope" to "Axis of related actual mating envelope".

Fig. 5-60 change "The center plane of datum feature B is perpendicular to datum plane A" to "Center plane of the related actual mating envelope of datum feature B perpendicular to datum plane A",

Fig. 5-61 change "The center plane of datum feature A" to "Center plane of the unrelated actual mating envelope of datum feature A".

Fig. 6-28 change "Regardless of feature size, the feature axis must lie between two parallel planes 0.2 apart which are inclined 60° to datum plane A. The feature axis must be within the specified tolerance of location" to "Regardless of feature size, the axis of the unrelated actual mating envelope of the feature of size must lie between two parallel planes 0.2 apart which are inclined 60° to datum plane A”.

Fig. 6-29 change "Regardless of feature size, the feature axis must lie within a 0.2 diameter cylindrical zone inclined 60° to datum plane A. The feature axis must be within the specified tolerance of location" to "Regardless of feature size, the axis of the unrelated actual mating envelope of the feature must lie within a 0.2 diameter cylindrical zone inclined 60° to datum plane A”.

Fig. 6-31 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". Change the note in the MEANS THIS to read "Regardless of feature size, the axis of the unrelated actual mating envelope of the feature must lie between two parallel planes 0.12 apart. The axis of the unrelated actual mating envelope must be within the specified tolerance of location."

Fig. 6-32 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". Change the note in the MEANS THIS to read "Regardless of feature size, the axis of the unrelated actual mating envelope of the feature must lie within a 0.2 diameter cylindrical zone parallel to datum axis A. The axis of the unrelated actual mating envelope must be within the specified tolerance of location."

Fig. 6-33 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". Change the note in the MEANS THIS to read "When the unrelated actual mating envelope is at its maximum material condition (10.00), the maximum parallelism tolerance is 0.05 diameter. Where the unrelated actual mating envelope of the feature departs from its MMC size, an increase in the parallelism tolerance is allowed which is equal to such departure. The axis of the unrelated actual mating envelope of the feature must be within the specified tolerance of location.



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Fig. 6-36 change "Possible orientation of feature center plane" to Possible orientation of center plane of unrelated actual mating envelope". Change the note in the MEANS THIS to read "Regardless of feature size, the center plane of the unrelated actual

Mating envelope of the feature must lie between two parallel planes 0.12 apart, which are perpendicular to datum plane A. The center plane of the unrelated actual mating envelope of the feature must be within the specified tolerance of location."

Fig. 6-37 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". Change the note in the MEANS THIS to read "Regardless of feature size, the axis of the unrelated actual mating

envelope of the feature must lie between two parallel planes 0.2 apart which are perpendicular to axis of the unrelated actual mating envelope of datum feature A. The axis of the unrelated actual mating envelope of the feature must be within the specified tolerance of location."

Fig. 6-38 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope".

Fig. 6-39 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". Change the note in the MEANS THIS to read "Regardless of feature size, the axis of the unrelated actual mating envelope of the feature must lie within a cylindrical tolerance zone 0.4 diameter, which is perpendicular to and projects from datum plane for the feature height. The axis of the unrelated actual mating envelope of the feature must be within the specified tolerance of location.

Fig. 6-40 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". In the note in the MEANS THIS change second and third sentences to read "Where the feature's unrelated actual mating envelope departs from its MMC size, an increase in the perpendicularity tolerance is allowed equal to the amount of such departure. The axis of the unrelated actual mating envelope must be within the specified tolerance of location."

Fig. 6-41 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". Change the note in the MEANS THIS to read "Where the unrelated actual mating envelope of the feature is at its maximum material condition (50.00), its axis must be perpendicular to datum plane A. Where the unrelated actual mating envelope of the feature departs from MMC, a perpendicularity tolerance is allowed which is equal to such departure. The axis of the unrelated actual mating envelope of the feature must be within the specified tolerance of location."

Fig. 6-42 change "Possible orientation of feature axis" to Possible orientation of axis of unrelated actual mating envelope". Change the note in the MEANS THIS to read "Where the unrelated actual mating envelope of the feature is at its maximum material condition (50.00), its axis must be perpendicular to datum plane A. Where the unrelated actual mating envelope of the feature departs from MMC, a perpendicularity tolerance is allowed which is equal to such departure, up to 0.1 maximum. The axis of the unrelated actual mating envelope of the feature must be within the specified tolerance of location."

global dimensioning and tolerancing addendum (gd&t) – 2004

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