British Standard Whitworth (BSW)

A symmetrical V thread with an angle between the threads measured in the axial plane of 55. 1/6 of the V, i.e. the point is truncated with arcs blended tangentially into the flanks. The following table lists tapping and clearance drill sizes in imperial and metric.

This thread form was developed by Sir Joseph Whitworth in 1841, the thread form is specified in BS 84: 1956. This thread form was superceded by first the Unified thread in 1948 and then the metric thread form.

BSW
Tapping Drill (65% engagement)Tapping Drill (100% engagement)Clearance Drill
Dia. [inches]TPIinchesmm inchesmminchesmm
1/16600.0481.240.0411.05  
3/32480.0761.940.0671.70  
1/8400.1042.60.0932.360.143.57
5/32320.133.30.1162.95  
3/16240.1523.90.1343.410.2035.16
7/32240.1844.70.1654.2  
1/4200.2085.30.1864.720.2656.75
5/16180.2666.80.2416.130.3268.3
3/8160.3238.20.2957.490.3899.9
7/16140.3789.60.3468.790.45211.5
1/2120.4310.90.39310.00.51513.1
9/16120.49312.50.45511.60.57814.7
5/8110.54914.00.50812.90.64116.3
3/4100.66616.90.62215.80.76719.5
7/890.78219.90.73218.60.88922.6
180.89622.80.8421.31.0225.8
11/871.00625.60.9423.91.1429
5/471.13128.71.06727.11.2732.2
3/261.36134.61.28632.71.51538.5
24.51.81546.11.71543.62.01551.2

Reference

BS 84:1956 "Specification for parallel screw threads of Whitworth form"

See also: Acme Thread, British Association Threads, British Standard Brass, British Standard Fine, Metric Threads, Model Engineers Thread, Thread, UNC, UNF, Whitworth, Joseph Sir.

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Subjects: Mechanical Engineering