Engineering Thread DataThreads

See Health & Safety Notice

Note: This information is produced for Model Engineers only. Commercial users should refer to the correct British or ISO standards as applicable. See Notes on British & International Standards

Screw fittings, essentially a matching internal & external constant pitch and diameter helix (female & male) form an essential part of society as we know it. It remains the ONLY practical way of joining individual elements in a secure, cheap way that can be assembled & disassembled as often as required. All this with the minimum of skill & tools. Threads used in situations where gas or liquid tightness is required can be tapered so as to lock up & seal on engagement.(BSP)

Threads were developed in many parts of the world, and as such produced a bewildering array of different standards. All attempts to "unify" the system only succeeded in producing yet another standard. Almost universal in the UK was BSF (British Standard Fine) BSW (British Standard Whitworth) & BA (British Association). As a leading manufacturer in the Industrial age British thread forms were exported around the world. The Motor Industry made an attempt to use the American " Unified Threads" (many UK car companies had strong US connections. Ford, Vauxhall etc.) but with the move to a European Union there has been a strong move to the Metric System (most of the large European car firms are indigenous, Audi, Fiat, Mercedes, BMW) etc. and it is almost 100% certain that in due course all the older mainstream threads will slowly fade away as the market for fittings and tools dies off, and costs rise to uneconomic levels. There is no signs of this as yet. (2005) America has been slow to embraced the Metric standards but will almost certainly go that way in due course.

As far as thread development is concerned the Metric form is almost certainly the end of the road. Unless there is some unforeseen technical development the Metric thread will continue to replace all other types. Virtually all new equipment will use the metric measurement system which will in turn mean the adoption of metric threads. Any remaining threads will be " metricated " ie: reissued in metric dimensions as the old imperial units disappear into the history books along with the rod, pole & perch. The older threads are usually designated "non-preffered"

As far as Model Engineering is concerned we can more or less do as we please. Much of our equipment is second hand and probably quite old and we have a need to be able to identify threaded items and fittings on a regular basis. We also have a thread of our own, the ME or Model Engineer thread. This is rather unique in only having two pitches for the entire range. 32tpi & 40tpi. and is based on the Whitworth form. Another curious feature of this thread is that you cannot buy commercial ME nuts & bolts, although steam & boiler fittings are very often ME. Check first. Another thread much used by model engineers is the BA thread. (British Association)

An attempt was made some while ago to introduce a set of metric standards for model engineering work. These are not a further set of standards, only a recommendation of suitable

sizes for model engineering work. They conform in all ways to the ISO standard. Taps & Dies are available.

A model engineer should have facilities to produce the full range of internal and external ME & BA threads together with a selection of BSW, BSF & the Metric Fine & Coarse threads up to at least ½" or M12 sizes. Other taps such as UNF, UNC BSP can be acquired as required.

Historical Archive

If required information can be supplied on the following threads:- British Standard Cycle, Loewenherz, Système International, Pipe & Sparking Plug, Square, Acme, BSP, Royal Microscopical Society, Royal Photographic Society, Waltham Watch, Watch Pendant, Watch Crown, Elgin Watch, Cordeaux, Edison Lamp Cap, Briggs Pipe, A.S.M.E, Holtzapffel's, Swiss Screw, American 8,12 & 16 pitch series, 20 Degree worm, Gas Threads, Progress Threads, SF French, French Standard, French Metric, German Metric & German Metric Fine.

Most if not all of these threads are well & truly obsolete.

Nomenclature

Left/Right Thread Types

Threads are normally Right Handed and unless otherwise stated this is the norm. This means that the nut screws on with a CLOCKWISE rotation. Left Hand threads are of course the opposite. Left Handed Threads are used extensively in the Motor Industry to secure rotating parts such as Drive Shafts, Gears etc. where the normal angular rotation would tend to tighten the nut. Left & Right Hand threads are used, as appropriate, on the Offside/Nearside of the Vehicle. When working on rotating parts always check the hand of the thread or consult the correct instruction manual. It is not uncommon for Wheel Nuts to be Left or Right handed. Use caution.

Thread Pitch

Usually expressed in threads per inch (tpi) or as an absolute dimension for one single pitch. ie 1mm. 0.2mm .75mm etc. Multi-start threads are basically the single start form, but with the pitch doubled etc. Very rare to come across these in model engineering.

Thread Included Angle.

Apart from a number of specialist threads the included angles for the most common threads are as follows. BA 47½°. BSW, BSF 55°. UNF, UNC, ANF, ANC 60°. Metric or ISO 60°. British Standard Cycle Thread (BSC) 60°. Acme 29°. Do not be tempted to use male & female threads with differing V angles. All the load is transferred to the thread crests and causes high stress levels, leading to slackening in service and premature failure.

Root & Crest Form

A major part of any thread is the crest & root form. Usually but not always this takes the form of a radius. Sometimes a flat. The root & crest form may also vary on the male & female threads. Production of a correct form, is for the average modeller virtually impossible. The

ISO Metric threads are however an exception. The standard allows for flat roots & crests (p/8 & p/4) It is possible to produce a "V" tool with a rounded root & let the crest remain as a flat. Where taps & dies are used the correct form is produced automatically.. When screw cutting it is now possible to buy ceramic tips that will automatically produce the correct root and crest radii. Since an insert is required for each form & pitch this puts their use outside the reach of most modellers due to cost. A 100% sharp "V" is undesirable as it may form the stress point for fracture and on bolts, cut fingers. Adding a small radius on the "V" tool with a stone is probably the best we can achieve. Another very good way is to use part of a new tap as a thread chaser & skim off the last few tenths & form the radii. Application of the correct root & crest radii does of course reduce the Actual thread depth compared to the full Theoretical Triangular "V" depth.

Effective or Pitch diameter.

On a parallel thread it is the diameter of an imaginary cylinder which would pass through the threads at such a point that both male and female thread were the same width. This point is usually but not always 1/2 the thread depth. It is only at 1/2 depth when the root & crest radii are the same.

Thread Identification.

With one or two exceptions (Lead screws, Vice Threads etc.) all the threads we meet are of the "V" form. Only the included angle varies and this is difficult to determine in the smaller sizes without special equipment. (Optical projectors etc.)

1) The first step is to determine the diameter and see if the thread is (or may be) Imperial or Metric. For example 5/16" & 8mm are very close together (only 2.5 thou !)

2) Next step is the pitch or threads per inch (tpi) If we ignore the fact that it may or may not be a metric thread, determine the number of threads in an inch. Lets say it comes to 25.5 approx. This equates to a 1mm pitch & if the dia was 6mm this is almost certain to be an ISO Metric Coarse M6 thread (ISO is the International Standards Organization) Thread pitch gauges, Taps, existing threads of known size etc. may be used. Try rolling the thread form onto a piece of paper and measure the pitch with an eyeglass & dividers.

3) If we can determine the thread included angle as 60° this clinches it. It is very difficult to establish what the thread angle is, but easy to state what it is not. For example if is bigger than 47½° & smaller than 60° it is almost certainly 55° and so on.

4) Determining the size of internal threads by direct measurement is (for the average modeller) virtually impossible. The best way is to try a selection of taps or threads until one fits perfectly without any slop or undue tightness. Unless you are working on safety critical or highly stressed components it will probably be OK. If possible make or buy a plug type gauge.

5) Look at the history of the item. Old British machinery, tools etc. probably BSF/BSW. Easy to tell apart by the pitches. Instruments/Electronics BA. Motor Cycle/Cycle BSC. USA, UNF/UNC. Continental ISO Metric etc. Old motor cars BSF/BSW, mid 50/60's UNF/UNC later models Metric.

Thread Data.

Please note that the figures given in the charts have been worked out from first principles and will NOT be exactly the same as those quoted in the ISO standards. The differences are usually only 1/10ths of thou.

Tables of threads are usually given in handy reference books but it is not generally known that all threads are based on a set formula for each thread.

Below is the formula for each thread and each type has a link to an WinZip Excel spreadsheet.. These charts are interactive and will give true thread details for any size required. By entering the required %age full thread a correct tapping size can be obtained. Select your nearest (very close) drill size. See Notes on the Data Sheets You may need to "unprotect" the data first.

Tapping Sizes

Some confusion often arises when different drill sizes are given to tap the same female thread. The reason is quite simple. There is no one drill size to tap a given hole !!

1) There may not be an exact drill size for the core diameter required. We use the nearest one available.

2) In practice it is usual to drill & tap to give a thread which is not 100% full thread. Figures such as 70%, 75%, 80% full thread are very rarely quoted but must have been used in the initial calculations

3) It is often desirable for the internal thread to have the crests flat rather than have the full perfect radiused form. This prevents threads binding & prolongs tool life.

4) When tapping hard material such as Stainless Steel an 70% full thread (female) used with a 100% male bolt may be 100% OK. Use a No.2 tap as less cutting length on the flutes reduces tap stress. Also consider modern coated taps.

5) It may be virtually impossible to tap 100% full thread anyway without risking a broken tap. If in doubt drill a tad bigger and use a good fitting male thread with more thread length engaged.

6) As with all things mechanical, tolerances must be mentioned. Tolerances are mainly the province of mass production & interchangeability. For our one off's, if it fits to YOUR SATISFACTION its OK. Thread tolerances can be a very complicated subject & need sophisticated gauging equipment. Taps are made in a range of tolerances. Class 2 is the normal specification. Carbon taps are usually cheaper & manufactured to wider tolerances. All taps are manufactured as "plus on basic" to allow for wear in production. As the tap wears the thread moves towards nominal.

7) Always use very sharp taps & dies & lubricate well.

8) It is virtually impossible to tap a hole 100% vertical by eye. Whenever possible, use a jig to ensure that the tap is vertical. Use of a tapping jig will virtually eliminate broken taps.

Health & Safety Notice

I recently read a note in quite a large Car & Motorcycle restoration guide that UNC & Whitworth nuts & bolts were interchangeable. This is complete rubbish & whilst some sizes are superficially the same ie: Pitch & Diameter, the Thread Angle IS NOT.(60/55) This means that all the load is directed onto the thread crests and roots and not full flank contact. DO NOT ATTEMPT TO MIX THE TWO. If in doubt throw away. One way to tell a UNF /UNC thread is to look for joined up circles on the flats of the nuts/bolts. ie: OOOOOO This is NOT however a 100% guide. I have also noticed UNF/UNC forged into the head. Another way is to use the Across Flats dimension. This is unique to UNC fasteners, it is not a whole metric size nor is it the same as the equivalent Whitworth fastener. Non of these methods are 100% reliable. Use a proper thread gauge if possible or try to measure the core diameters with the correct thread micrometer. If the fit is tight or loose it is probably an incorrect mix. Also note that Stainless Steel fittings ARE NOT AS STRONG as HIGH TENSILE steel bolts etc. DO NOT USE in highly stressed applications where bolt failure could lead to an accident without full professional advice as to grade, thread form and suitable diameter. If in doubt always use the Manufacturer's correct part for the relevant application.

Thread Data & Formulae

BSW (British Standard Whitworth)

P = Pitch = 1/Number of threads per inch (tpi)

h = Angular Depth = 0.960491 x P

D = Depth of Rounding = 0.073917 x P

h/6 = Shortening = 0.160083 x P

d = Actual Depth = 0.640327 x P

r = Radius at the Crest & Root = 0.137329 x P

C = Core diameter = Major Diameter - 1.280654 x P

Effective or Pitch Diameter = Major Diameter - .640327 x P

BSF (British Standard Fine)

P = Pitch = 1/Number of threads per inch (tpi)

h = Angular Depth = 0.960491 x P

D = Depth of Rounding = 0.073917 x P

h/6 = Shortening = 0.160083 x P

d = Actual Depth = 0.640327 x P

r = Radius at the Crest & Root = 0.137329 x P

C = Core diameter = Major Diameter - 1.280654 x P

Effective or Pitch Diameter = Major Diameter - .640327 x P

ME (Model Engineer)

P = Pitch = 1/Number of threads per inch (tpi)

h = Angular Depth = 0.960491 x P

D = Depth of Rounding = 0.073917 x P

h/6 = Shortening = 0.160083 x P

d = Actual Depth = 0.640327 x P

r = Radius at the Crest & Root = 0.137329 x P

C = Core diameter = Major Diameter - 1.280654 x P

Effective or Pitch Diameter = Major Diameter - .640327 x P

BA (British Association)

P = Pitch = 1/Number of threads per inch (tpi)

h = Triangular height = 1.1363365 x P

d = Actual Depth = 0.60000 x P

t = Shortening = 0.2681688 x P

r = Radius at the Crest & Root = 0.1808346 x P

Effective or Pitch Diameter = Major Diameter - 0.6000 x P (d)

C = Core diameter = Major Diameter - 1.2000 x P (2d)

Nuts and Bolts across flats is nominally 1.75 x Major Diameter

For Model Engineering purposes nuts and bolts are obtainable

with the hexagon heads one size less across flats, this gives a better scale effect.

ISO Metric Fine

ISO Metric Coarse

P = Pitch = 1/Number of threads per inch (tpi)

H = Angular Depth = 0.866025 x P

H/8 = Shortening of major dia = 0.108253 x P

H/4 = Shortening of minor dia = 0.216506 x P

d = Actual Depth = 0.541266 x P

r = Radius at the Root = 0.1443 x P

Hn = Basic height of Internal Thread = 0.54127 x P

Hs = Basic height of External Thread = 0.61344 x P

Note: The form of the Metric Series of Threads varies between Internal & External Threads, in particular the root and crest details. This allows for flat (truncated) or radiused forms. Engineers requiring more specific information should refer to the relevant ISO Standards. This data base is far to small to fully cover this subject.

Unified National Fine (UNF)

Unified National Coarse (UNC)

P = Pitch = 1/Number of threads per inch (tpi)

H = Angular Depth = 0.866025 x P

H/8 = Shortening of major dia = 0.108253 x P

H/4 = Shortening of minor dia = 0.216506 x P

d = Actual Depth = 0.541266 x P

r = Radius at the Root = 0.1443 x P

Hn = Basic height of Internal Thread = 0.54127 x P

Hs = Basic height of External Thread = 0.61344 x P

United States Standard (USS)

United States Form (USF)

Society of Automobile Engineers (SAE)

This form also occurs in the National Coarse (N.C.) and National Fine (N.F.) series of threads.

It is very similar to the UNF and UNC threads but has a Flat Root & Crest.

P = Pitch = 1/Number of threads per inch (tpi)

H = Theoretical Depth = 0.866 x P

D = Actual Depth = 0.6495 x P

F = Width of Flat = 0.125 x P

A = Depth of Flat = 0.108 x P

Sharp V-thread. (V)

Details for this thread were taken from Machinery Handbook 9th Edition (1938) pg 1146. This thread has been noted on older Harley Davidson Motorcycles and is understood to have been used on older US Cadillac Automobiles.

Due to the sharp root and crest on this form, it is in theory, prone to stress cracking. The later UNF/UNC threads should be used where possible, as these have rounded crests and roots, thus reducing stress concentration. The "V" thread is effectively obsolete. It still remains a very easy thread to cut using single point tools. It is however NOT interchangeable with modern 60 degs Imperial threads. UNF/UNC etc. Cutting tools, Taps and Dies etc. are no longer available.

The sides of the thread form an angle of 60 degs with each other. The top and bottom of the threads are theoretically sharp, but in practice the crest has a slight flat equal to 1/25th x Pitch. This is removed after the thread is cut, thus reducing the actual diameter slightly below nominal. (D) See chart details.

P = Pitch = 1/Number of threads per inch (tpi)

H = Theoretical Depth = 0.866 x P

D = Actual Depth with Crest Relief

A= Width of Flat = P/25 (Not in the Official Standards)

N = Depth of Flat

Notes on British & International Standards

Hard copies of ISO/British Standards are very expensive, typically £30 for a single copy. Less if you are a BSI member. Most large libraries now have Internet Access & seem to have an agreement with the ISO/BSI. This means that you can view any standard, but as far as I

am aware, you are not able to make copies. Thread standards are by their very nature complex documents and unless you are working in a standards room or are a manufacturer of tooling etc. contain large amounts of data irrelevant to model engineers work. Most of the older non metric threads have been designated as " non-preferred thread series " for many years. They should be avoided in new equipment etc.

Notes on the Data Sheets

The data sheets can be downloaded as Zip files into an Excel Spreadsheet. All files are in the protected mode. Some files have a figure in red over the tapping size. This represents the %age full thread. This can be altered to give a tapping size to suit the thread you require. eg. on Aluminum you may wish to tap 100% full thread. You can also use the data to give full details of non-standard threads such as the Myford Nose etc. By entering the diameter & pitch all the other details self calculate. No responsibility can be accepted for errors or omissions by whatever cause.

RECOMMENDED DRILL SIZES

FOR

SELF-TAPPING SCREWS (SHEET METAL)

Self-Tapping Screw Size

Major Thread Diameter

Minor Thread Diameter

For Heavy Metals

For Light Metals

No. Threads per Inch

O.D. Max. Mean  Min. Max.  

Mean Min. Drill Size Drill Size

2 32 .086 .088 .0850 .082 .064 .0620 .060 49 .0730 49 .0730

4 24 .112 .114 .1110 .108 .086 .0840 .082 41 .0960 41 .0960

5 20 .125 .130 .1265 .123 .094 .0920 .090 36 .1065 36 .1065

6 20 .138 .139 .1355 .132 .104 .1015 .099 32 .1160 32 .1160

7 19 .151 .154 .1505 .147 .115 .1120 .109 30 .1285 30 .1285

8 18 .164 .166 .1625 .159 .122 .1190 .116 28 .1405 29 .1360

10 16 .190 .189 .1855 .182 .141 .1380 .135 20 .1610 21 .1590

12 14 .216 .215 .2115 .208 .164 .1605 .157 13 .1850 14 .1820

1/4 14 .250 .246 .2415 .237 .192 .1885 .185 3 .2130 4 .2090

5/16 12 .313 .315 .3105 .306 .244 .2400 .236 I .2720 H .2660

3/8 12 .375 .380 .3755 .371 .309 .3040 .299 R .3390 Q .3320

Across Flats Engineering DataSpanner sizes

Information on the across flats dimensions of nuts and bolts in common use seems quite hard to find. There are so many thread types still in circulation, and almost without exception, all use quite independent across flats sizes. Metric threads use whole metric numbers. 17, 19, 20 etc. UNF/UNC go for Imperial fractional sizes. 5/8", 1/2" etc. BA, Whit & BSF seem to use a decimal size with no easy fractional base. 0.445", 0.710", 1.100" etc. The now obsolete across flats sizes relate direct to the spanner !! Comparison of across flats dimensions shows that, for correct practice, there are very few spanners that are truly multi thread. As with all matters engineering the empirical method is usually the best. If the spanner/socket is a good fit, use it. No official across flats dimensions are given for ME ( Model Engineer ) threads as nuts and bolts are not commercially available. Figures given are the editors own based on the BA formulae. In the BA sizes it is possible to buy nuts etc with a size less across flats. ie: 2BA with 3BA dimensions. This gives a better scale effect, where strength is not important. The Across Flats zipped file gives Spanner ( & Socket ) sizes in ascending order, very good to see if your "nearest size" is near enough. If you are considering the manufacture of odd nuts & bolts, make sure that a suitable hexagon bar is available. Milling flats on dozens of nuts & bolts is not my idea of a good time ? Go to Across Flats Database.

Note:- At one time Whit & BSF across flats sizes were the same. ie a 5/16"Whit & 5/16 BSF across flats was the same. As an economy measure during WWII it was decided to reduce the across flats sizes of Whitworth nute and bolts by one size. Thus a 5/16" Whit across flats was the same as a 3/8" BSF. Also note that the core diameter for a Whitworth thread is less than the same size in BSF. (Coarser thread pitch, hence deeper threads)

http://www.maintenanceengineering.in/Fastners.php

FASTENERS

Fasteners are a simplest mechanical device to join two or more elements

without welding e.g. with Nuts & Bolts, Studs & Nuts and Screw etc. There

are internal and matching external threads on the fasteners, which

actually takes the load. These threads play an important role in sharing

the load of application. There are various kind of internal and external

threads designed according to the application/requirements.

UNIFED AND ISO THREAD GEOMETRY

Definitions:

Pitch (p)- The distance between adjacent thread forms measured parallel

to the thread axis.

TPI (n) - The number of Threads per Inch related to the pitch by p = I/n.

Root (minor) Diameter - Smallest diameter of screw - d

Major Diameter - Largest diameter of screw - dc(sometimes designated as

d).

Mean (pitch) Diameter - Average diameter of screw - dm(sometimes

designated as dp).

Lead Angle ( ) - The angle defining the inclination of the thread (See figure

below).

Helix Angle ( ) - The angle between the thread axis and the lead angle

.

A-FULL DIAMETER SHANK:

Equal to major diameter of thread. Produced by cut thread or by roll

thread on extruded blank. Characteristic of machine bolts and cap

screws.

B-UNDERSIZED SHANK:

Equal approximately to pitch diameter of thread. Produced by roll

threading a non-extruded blank. Characteristic of machine screws.

D-PITCH DIAMETER: The simple, effective diameter of screw thread.

Approximately half way between the major and minor diameters.

E-MAJOR DIAMETER: The largest diameter of a screw thread.

F-MINOR DIAMETER: The smallest diameter of a screw thread.

LEAD: The distance a screw thread advances axially in one turn.

CUT THREAD: Threads are cut or chased; the unthreaded portion of

shank will be equal to major diameter of thread.

ROLLED THREAD: Threads are cold formed by squeezing the blank

between reciprocating serrated dies. This acts to increase the major

diameter of the thread over and above the diameter of unthreaded

shank (if any), unless an extruded blank is used.

Classes of thread are distinguished from each other by the amounts of

tolerance and allowance specified. External threads or bolts are

designated with the suffix "A"; internal or nut threads with "B".

THREADS OF A FASTENERS

There are many type of Internal and External threads are in use in

industries, depending upon the requirement. Internal threads may be

made as tapped by high-speed-steel tap set or machined. External

threads may by made by die cut or machined or rolled-in-die under

hydraulic pressure. For threaded dimension of metric threads ANSI/ASME

B18.2.3.5M or B 18.2.3.6M standard are followed and for mechanical

property ASTM F568M, ASTM F486M, ASTM F738M etc. are followed

widely.

The type of thread of a screw or bolt or stud depends upon the material of

construction, dynamic load, vibration, torque required etc.

Threads are classified as:

1) coarse thread,

2) Fine thread or

3) extra fine thread for specific uses.

The clearance between a male thread and matching female thread are

covered under class or fit as prescribed by various international

standards. Some widely used threads are given below :-

UNC - Unified National Coarse

UNF - Unified National Fine

UNEF - Unified National Extra Fine

USN - Unified National Special

UNR - Unified National Round (round root)

ISO - Internatinal Standards Organization (metric)

BSW - British Standard Whiteworth

BSF - British Standard Fine

BSP - British Standard Pipe

NPT - National pipe thread

For stud and bolt and their matching counter parts, normally BSW, UNC,

UNF or BSF threads are commonly used depending upon the application,

however for piping systems BSP or NPT threads are used internationally.

NPT system is used in more countries than BSP system. UNF threads are very fine pitch threads (more threads per inch) than UNC or UNR or BSW. These threads are used where higher torque values are to be used or the system is working in high vibration mode. E.g. in high pressure reciprocating compressors.

The basic difference between piping thread system BSP and NPT is that

the later is tapered. NPT threads are generally used in high pressure

instrumentation fitting e.g. pressure gauge pressure tapping etc. BSP

generally used in low-pressure services.

UNR threads are just like UNC thread but the crest are rounded off and

can take more compressive and tensile load then UNC and fatigue

strength are also high. These threads are used on Puller rods. These are

only external threads. The UNR external threads are rolled UN threads in

all respects except that the root radius must be rounded.

UNF :- UNF Thread has large minor diameters than UNC thread which

gives UNF fastener slightly higher load carrying capacity and better torque

locking than UNC. The fine threads have tighter tolerance than UNC

thread.

Quality of threads is important for the load bearing capacity of the bolting

system. Domestic quality threads can not be used in critical industrial

service. Thread quality is defined as thread class which specifies the

allowable tolerance and clearance between the mail and female threads

known as installation fit.

THREAD CLASS :- There are three classes for external threads

designated as 1A. 2A & 3A and similarly for internal threads class are

designated as 1B, 2B & 3B. Generally same category of class for both type

of threads are selected for a particular service.

CLASS 1A AND 1B :- These are the loosest fit bolting systems and have

largest amount of play between the male and female parts of the

assembly. This class is used only in domestic use bolting system and in

structural assemblies.

CLASSES 2A AND 2B :- This class is specified for the typical fit where

reasonable quality and fit predictability is required and most widely used

in industrial fasteners.

CLASS 3A AND 3B :- This class is specified for high quality precession

application of fasteners e.g. in measuring / calibration instruments etc.

Threaded stud specification :- It is always important to give correct

specifications for getting the threaded studs exactly as per requirement.

Specifications shall cover the thread size, length of stud, type of threads,

class of threads, material class & grade Material class & grade of nut etc.

Examples:

i) SWN 1/4”X95, 20 UNC 2A, A193 B7/A194 2H Which read as “ stud with

nuts, size 1/4”, length 95mm, threads as per 20 TPI in UNC in thread class

2A, material as per ASTM A193 Grade B7 and Nuts as per ASTM A194

Grade 2H.”

ii) BWN 5/8”X110, UNC 2A, A193 B16/A194 4H Which read as “ Bolt with

nut, size 5/8”, length 110mm, threads as per UNC in thread class 2A,

material as per ASTM A193 Grade B16 and Nuts as per ASTM A194 Grade

4H.”

EQUIVALENT IMPERIAL THREAD TOLERENCE & CLASSSES :- There

are certain equivalent tolerance and fits in Imperial internal/external

thread and ISO thread tolerance class. E.g. Imperial fit tolerance class

2B/2A is equivalent to 6H/6g of ISO thread tolerance class. Class fit 3B/3A

is approximately equivalent of ISO class fit 4H5H/4h6h In ISO thread

classes details are covered in ISO 965-1 Sec 2.7 & 12.

FAILURE OF FASTENER :- Any fastener joint failure on a machine or on

a process piping or on a stationery equipment can have potentially

disastrous consequences. Therefore it is very important to select and use

appropriate fastener of proper material, proper thread type and thread

classes as well as torque applied for tightening. Failure of a threaded

fastener generally occurs in three modes.

i) Failure by tensile fracture through the shank or threaded section.

ii) Shear failure through the threaded (thread stripping) of external thread.

iii) Shear failure through the thread profile of the internal threaded

portion.

Thread stripping is a shear failure of an internal or external thread that

results when the strength of the threaded material exceeded by the

applied force acting on the threads. Thread stripping tends to be gradual

in nature and it may go unnoticed at the time of assembly. Improper

fitment, abnormally small length of nut also leads to thread stripping. Selection of Material For Fastners

Temperature Range Material Bolt/ Nut 100°C - 200°C A320B8/Gr .8 46°C - 100°C A320L7/Gr .4 0°C - 45°C A320L7/Gr .4

SNB7/S45C 0°C - 300°C A307 SS400

300°C - 400°C A193B7/Gr .2HB7/2HSNB7/S45C

400°C - 550°C A193B16/Gr .4

550°C - 650°C A193B8/Gr .8 A193B8M/Gr .8M

650°C A453Gr.660,A453Gr.660/Gr 8C

750°C Hastalloy B & C High Temperature High Tension Alloy Bolt Material Chemical & Mechanical Requirements

ASTM A193 B7 ( Cr- Mo AISI 4140,4142,4145 )This material is considered as the most suitable for bolts to be used at temperature below 450 °. C, with a minimum effect on its structural strength during application at a high temperature.The material has the following chemical properties and physical Characteristics

ASTM A1193 B7M ( Cr- Mo AISI 4140,4142,4145 )

C Mn P S Si Cr Mo

0.37-0.49

0.65-1.10 0.035 Max

0.04 Max 0.15-0.35

0.75-1.20 0.15-0.25

Dia

MinimumTempering Temperat

ure ° F (°C)

TensileStrengthmin, ksi

MPa

YieldStrength.

min,0.2% offset,

Ksi

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

21/2" and

under

1150(620 ° C )

100(690) 80(550) 18 50 235HB, 99HRB

ASTM A193 B16 (Cr- Mo -V )This material is considered as the most suitable for bolts to be used at temperature below 450 °. C,even at a high temperature range, the material has superior physical characterestics compared to ASTM A193 B7 previously mentioned.The chemical properties and physical characteristics are as follows

C Mn P S Si Cr Mo Al V

0.36-0.47

0.45-0.70 0.035 Max

0.04 Max

0.15-0.35

0.80-1.15

0.50-

0.65

0.015Max

0.25-

0.35

Dia

MinimumTemperat

ure ° F (°C)

TensileStrengt

hmin, ksi( MPa)

YieldStrength. min,0.2% offset,

Ksi( MPa)

Elongation in

4Dmin %

Reduction ofArea

min %

Hardnessmax

21/2"

and unde

r

1200(650) 125(86

0) 105(72

5) 18 50

321HBor 35 HRC

over 21/2" to 4"

1200(650) 110(76

0) 95(655) 17 45

302HBor 33 HRC

over 4" to

7"

1200(650 )

100(690)

85(586) 16 45 227HB

or 29 HRC

ASTM A193 B5 (5% Cr AISI 501)

C Mn P S Si Cr Mo

0.10 max 1.00 max 0.040 max

0.030 Max

1.0 Max 4.00 - 6.00

0.40 -0.65

Dia

MinimumTempering Temperat

ure° F (°C)

TensileStrengthmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

up to 4" incl

1.100 (593 )

100(690) 80(550) 16 50 -

ASTM A193 B8 (AISI 304) B8A Chemical Requirements

C Mn P S Si Cr Ni

0.08 Max 2.00 Max 0.045 Max

0.030 Max

1.00 Max 18.00 - 20.00

8.00 -10.50

ASTM A193 B8C (AISI 347) B8CA

C Mn P S Si Cr Ni Columbiu

m +Tantalum

0.08 Max

2.00 Max

0.045 Max

0.030 Max

1.00 Max

17.00 - 19.00

9.00 -13.00

10 x Carboncontent,

min

ASTM A193 B8N (AISI 304N) B8NA

C Mn P S Si Cr Ni Nitroge

n

0.08 Max

2.00 Max

0.045 Max

0.030 Max

1.00 Max

18.00 - 20.00

8.00 -10.50

0.10 - 0.16

ASTM A193 B8MN (AISI 316N) B8MNA

C Mn P S Si Cr Ni Mo Nitroge

n

0.08 Max

2.00 Max

0.045 Max

0.030 Max

1.00 Max

16.00 - 18.00

10.00 -14.00

2.00 - 3.00

0.10 - 0.16

ASTM A193 B8P (AISI 305) B8PA

C Mn P S Si Cr Ni

0.08 Max 2.00 Max 0.045 Max

0.030 Max

1.00 Max 17.00 - 19.00

10.50 -13.00

ASTM A193 B8T (AISI 321) B8TA

C Mn P S Si Cr Ni Titaniu

m

0.08 Max

2.00 Max

0.045 Max

0.030 Max

1.00 Max

17.00 - 19.00

9.00 -12.00

5 x Carboncontent,

min

ASTM A193 B8R B8RA

C Mn P S Si Cr Ni Mo Nitroge

n

Columbium+

Tanalum

V

0.06 Max

4.00 -

6.00

0.040

Max

0.030

Max

1.00 Max

20.50 -

23.50

11.50 -

13.50

1.50 -

3.00

0.20 - 0.40

0.10 - 0.30

0.10 - 0.30

ASTM A193 B8S B8SA

C Mn P S Si Cr Ni Nitroge

n

0.10 Max

7.00 - 9.00

0.040 Max

0.030 Max

3.50 - 4.50

16.00 - 18.00

8.00 - 9.00

0.08 - 0.18

ASTM A193 B8LN, B8LNA

C Mn P S Si Cr Ni Mo Nitroge

n

0.030 Max

2.00 0.045 Max

0.030 Max

1.00 18.00 - 20.00

8.00 - 10.50

- 0.10 - 0.16

B8MLN, B8MLNA

C Mn P S Si Cr Ni Mo Nitroge

n

0.030 Max

2.00 0.045 Max

0.030 Max

1.00 16.00 - 18.00

10.00 - 14.00

2.00 - 3.00

0.10 - 0.16

CLASS I: B8, B8C, B8M, B8P, B8T, B8LN, B8MLN Mechanical Requirements

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

All diamete

rs

Carbide Solution Treated

75(515) 30(205) 30 50

223 HB or 96HRB

(3/4" in & smaller,

241HB or 100 HRB)

CLASS IA: B8A, B8CA, B8MA, B8PA, B8TA, B8LNA, B8MLNA, B8NA, B8MN4

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

All diamete

rs

Carbide Solution

Treated in the finished

75(515) 30(205) 30 50 192 HB or 90HRB

conditions

CLASS IB: B8N, B8MN

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

All diamete

rs

Carbide Solution Treated

80(550) 35(240) 30 40

223 HB or 96HRB

(3/4" in & smaller,

241HB or 100 HRB)

CLASS IC: B8R

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

All diamete

rs

Carbide Solution Treated

100(690)

55(380) 35 55 271 HB

or 28 HRC

CLASS IC: B8RA

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

All diamete

rs

Carbide Solution

Treated in the finished

condition

100(690)

55(380) 35 55 271 HB

or 28 HRC

CLASS IC: B8S

Dia Heat Tensile Yield Elongati Reductio Hardness

Treatement

Strength

min, ksi(MPa)

Strength. min,0.2% offset,

Ksi(MPa)

on in 2"

min %

n ofArea

min % max

All diamete

rs

Carbide Solution Treated

95(655) 50(345) 35 55 271 HB

or 28 HRC

CLASS IC: B8SA

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

All diamete

rs

Carbide Solution

Treated in the finished

condition

95(655) 50(345) 35 55 271 HB

or 28 HRC

CLASS 2: B8, B8C, B8P, B8T, B8N

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardnessmax

3/4" & under

Carbide Solution Treated

andstrain

Hardened

125(860)

100(690) 12 35

321 HBor 35 HRC

over 3/4" & 1" incl

115(795)

80(550) 15 35

over 1" & 11/4" incl

105(725)

65(450) 20 35

11/4" to 11/2" incl

100(690)

50(345) 28 45

CLASS 2: B8MN / B8M

Dia Heat Treateme

TensileStrengt

YieldStrength.

Elongation in

Reduction of

Hardnessmax

nt h

min, ksi(MPa)

min,0.2% offset,

Ksi(MPa)

2"min %

Areamin %

3/4" & under

Carbide Solution

Treatedand

strainHardened

110(760)

95(655) 15 45

321 HBor 35 HRC

over 3/4" & 1" incl

100(690)

80(550) 20 45

over 1" & 11/4" incl

95(655) 65(450) 25 45

11/4" to 11/2" incl

95(655) 75(515) 25 40

CLASS 2B: B8M2

Dia Heat

Treatement

TensileStrengt

hmin, ksi(MPa)

YieldStrength.

min,0.2% offset,

Ksi(MPa)

Elongation in

2"min %

Reduction ofArea

min %

Hardness°max

2" & under

Carbide Solution Treateda

ndstrain

Hardened

95(655) 75(515) 25 40

321 HBor 35 HRC

over 2" & 21/2" incl

90(620) 65(450) 30 40

over 21/2" to 3" incl

80(550) 55(380) 30 40