Technical

The technical information on this page is provided for general informational purposes only. While Thomas Smith Fasteners strives for accuracy, there are no guarantees of completeness, reliability, or timeliness. The information should not replace professional advice. Consult a qualified professional for specific guidance. Contact our technical sales team for help.

Specifications and standards in the fastener industry may change. Thomas Smith Fasteners is not liable for any outdated information or for any damages resulting from the use of this website.



​​Dimensional Specifications

DIN 931 & DIN 933

The drawing below shows unthreaded fasteners. The thread length of Metric bolts manufactured to DIN 931 and 933, with diameter d and thread length t, is:

t = 2d + 6mm up to 125mm; t = 2d + 12mm from 125mm until 200mm; 2d + 25mm at 200mm and over.

BS 1083

The drawing below shows unthreaded fasteners. The thread length of BSW or BSF bolts manufactured to BS1083, with diameter d and thread length t, is t = 2d.

BS 1768

The drawing below shows unthreaded fasteners. The thread length of UNC or UNF bolts manufactured to BS1768, with diameter d and thread length t, is: t = 2d + 1/4" up to a length of 6", where the formula becomes t = 2d + 1/2".



How to measure

Measuring bolt diameter

Bolts can be accurately measured using a vernier. For metric bolts, the prefix 'M' is added to denote Metric. For example, a 4mm diameter bolt is commonly known as an 'M4' bolt. Imperial bolts are measured in inches.

Measuring bolt length

The length of a Hexagon bolt is determined by measuring from underneath the head to the end of the bolt. If the bolt has a countersunk head, the full length of the bolt including head is measured.

Measuring threads

Metric bolts are identified by measuring the distance between the threads - a 1mm pitch bolt has 1mm between the threads. The thread pitch of an imperial bolt is denoted by the amount of threads per inch. See the thread charts on this page for more information. A thread gauge can be used to identify bolts and nuts, although they are not in common usage. The Thread Detective is a quick and easy solution to the problem of identifying bolt and nut threadforms, allowing quick and precise identification of Metric, UNC & UNF bolts and nuts.



 


 

Thread Charts

Metric

Metric bolts are identified by measuring the distance between the threads in millimetres - a 1mm pitch bolt has 1mm between the threads.

DiameterCoarseFineExtra FineSuper Fine
M10.250.2  
M1.60.350.25  
M20.40.25  
M2.50.450.35  
M30.50.35  
M40.70.5  
M50.80.5  
M61.00.75  
M71.00.75  
M81.251.00.75 
M101.51.251.00.75
M121.751.51.251.0
M142.01.51.251.0
M162.01.51.0 
M182.52.01.51.0
M202.52.01.51.0
M222.52.01.51.0
M243.02.01.51.0

Imperial

The thread pitch of an imperial bolt is denoted by the amount of threads per inch.

DiameterUNCUNFBSWBSF
No.44048  
No.63240  
No.10 / 3/1624322432
1/420282026
5/1618241822
3/816241620
7/1614201418
1/213201216
9/1612181216
5/811181114
3/410161012

BA

BA is an imperial threadform. The thread pitch of an imperial bolt is denoted by the amount of threads per inch.

BA NumberTPIDia (inch)
647.90.11
438.50.142
334.80.161
231.40.185
025.40.236



 

Mechanical Properties

Metric

Property4.68.8 <= M168.8 > M1610.912.9
Min Tensile N/mm240080083010401220
Min Lower Yield Stress N/mm2240    
Min Proof Stress N/mm2 6406609401100
Hardness Min HRC 22233239
Hardness Max HRC 32343944

BSW & BSF

PropertyRTV
Min Tensile tonf/in2455565
Min Yield Stress tonf/in2344152
Hardness Brinell201/285248/335293/370

UNC & UNF

PropertyRTV
Min Tensile tonf/in2505565
Min Yield Stress tonf/in2384149.5
Hardness Brinell223/310248/335293/370



 

Torque Figures

Metric Coarse

 M6M8M10M12M14M16M20M22M24M30M36M42
4.6 kgf m0.461.122.233.896.219.6518.825.632.664.7113181
8.8 kgf m1.233.05.9510.3516.525.750.268.386.6172300478
10.9 kgf m1.734.228.3514.623.236.270.796122242423678

Metric Fine

 M6M8M10M12M14M16M20M22M24M30M36
4.6 kgf m0.501.202.354.246.7210.320.928.135.471.5120
8.8 kgf m1.343.26.2511.317.927.355.775.094.5189316
10.9 kgf m1.904.528.815.925.238.578.5105132268448

UNC

 1/45/163/87/161/29/165/83/47/811.1/81.1/41.3/81.1/2
S ibf ft9203556851231703004857301035146019202540
T ibf ft10213658881271753115007501065150019652610
V ibf ft122545731111602123936329501345190024803300

UNF

 1/45/163/87/161/29/165/83/47/811.1/81.1/41.3/81.1/2
S ibf ft11224062961371923355357951075150020402690
T ibf ft12234164991411953456508201100154021002760
V ibf ft1428508112518023843569510001390195026503500

BSW

 1/45/163/87/161/29/165/83/47/811.1/81.1/41.3/81.1/2
R ibf ft8173047701051452554106208751235-2150
V ibf ft1225457210716021039062894513301890-3280

BSF

 1/45/163/87/161/29/165/83/47/811.1/81.1/41.3/81.1/2
R ibf ft918325177112155268432650930130017302270
V ibf ft142749781181732244106609951420199026303480

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