Whitworth & British

Whitworth Instrument Thread

British threads based on Whitworth's 55° profile with rounded crests and roots, still found on older machinery, pipe fittings and model engineering.

Flank angle: 55°
Sizes listed: 32
Range: 10 – 100

Profile shape (schematic, not to scale)

Thread No.	Major Diameter mm	Major Diameter Inch	Pitch mm	TPI	Tapping Drill Size mm
10	0.254	0.010	0.064	400	0.173
11	0.279	0.011	0.064	400	0.198
12	0.305	0.012	0.073	350	0.212
13	0.330	0.013	0.073	350	0.237
14	0.356	0.014	0.085	300	0.247
16	0.406	0.016	0.085	300	0.298
17	0.432	0.017	0.102	250	0.302
18	0.457	0.018	0.102	250	0.327
19	0.483	0.019	0.102	250	0.353
20	0.508	0.020	0.121	210	0.353
22	0.559	0.022	0.121	210	0.404
24	0.610	0.024	0.121	210	0.455
26	0.660	0.026	0.141	180	0.480
28	0.711	0.028	0.141	180	0.531
30	0.762	0.030	0.141	180	0.581
32	0.813	0.032	0.141	180	0.632
34	0.864	0.034	0.169	150	0.647
36	0.914	0.036	0.169	150	0.698
38	0.965	0.038	0.212	120	0.694
40	1.016	0.040	0.212	120	0.745
45	1.143	0.045	0.212	120	0.872
50	1.270	0.050	0.254	100	0.945
55	1.397	0.055	0.254	100	1.072
60	1.524	0.060	0.254	100	1.199
65	1.651	0.065	0.318	80	1.245
70	1.778	0.070	0.318	80	1.372
75	1.905	0.075	0.318	80	1.499
80	2.032	0.080	0.423	60	1.490
85	2.159	0.085	0.423	60	1.617
90	2.286	0.090	0.423	60	1.744
95	2.286	0.095	0.508	50	1.636
100	2.540	0.100	0.508	50	1.890

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Reference values only. Verify against the current edition of the governing standard before use in production drawings or manufacturing. Provided by Micro Components as a free engineering resource.

Whitworth Instrument Thread

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