Historic Bolt Sizes

British Standard Whitworth bolt sizes and cross sectional areas are given in the table below:

*British Standard Whitworth (Inches)*
Diameter (inches)	Threads per inch	Diameter at bottom of thread (inches)	Area at bottom of thread (inches²)	Heaxagon Head and Nut			Thickness of Head (inches)		Thickness of Nut (inches)
				Width across flats (inches)		Approx Across Corners (inches)	Thickness of Head (inches)		Thickness of Nut (inches)
				Min.	Max.	Approx Across Corners (inches)	Min.	Max.	Min.	Max.
¹⁄₄	20	0.1860	0.0272	0.520	0.525	0.61	0.21	0.22	0.240	0.250
⁵⁄₁₆	18	0.2414	0.0458	0.595	0.600	0.69	0.26	0.27	0.302	0.312
³⁄₈	16	0.2950	0.0683	0.705	0.710	0.82	0.32	0.33	0.365	0.375
⁷⁄₁₆	14	0.3460	0.0940	0.815	0.820	0.95	0.37	0.38	0.427	0.437
¹⁄₂	12	0.3933	0.1215	0.915	0.920	1.06	0.43	0.44	0.490	0.500
⁹⁄₁₆	12	0.4558	0.1632	1.002	1.010	1.17	0.48	0.49	0.552	0.562
⁵⁄₈	11	0.5086	0.2032	1.092	1.100	1.27	0.54	0.55	0.615	0.625
¹¹⁄₁₆	11	0.5711	0.2562	1.192	1.200	1.39	0.59	0.60	0.677	0.687
³⁄₄	10	0.6219	0.3038	1.292	1.300	1.50	0.65	0.66	0.740	0.750
⁷⁄₈	9	0.7327	0.4216	1.468	1.480	1.71	0.76	0.77	0.865	0.875
1	8	0.8399	0.5540	1.658	1.670	1.93	0.87	0.88	0.990	1.000
1¹⁄₈	7	0.9420	0.6969	1.845	1.860	2.15	0.96	0.98	1.105	1.125
1¹⁄₄	7	1.0670	0.8942	2.035	2.050	2.37	1.07	1.09	1.230	1.250
1³⁄₈	6	1.1616	1.0597	2.200	2.220	2.56	1.18	1.20	1.355	1.375
1¹⁄₂	6	1.2866	1.3001	2.390	2.410	2.78	1.29	1.31	1.480	1.500
1⁵⁄₈	5	1.3689	1.4718	2.555	2.580	2.98	1.40	1.42	1.605	1.625
1³⁄₄	5	1.4939	1.7528	2.735	2.760	3.19	1.51	1.53	1.730	1.750
2	4.5	1.7154	2.3111	3.125	3.150	3.64	1.73	1.75	1.980	2.000

British Standard Whitworth bolt sizes and cross sectional areas, converted to mm, are given in the table below:

*British Standard Whitworth (Converted to mm)*
Diameter (inches)	Diameter (mm)	Threads per mm	Diameter at bottom of thread (mm)	Area at bottom of thread (mm²)	Heaxagon Head and Nut			Thickness of Head (mm)		Thickness of Nut (mm)
					Width across flats (mm)		Approx Across Corners (mm)	Thickness of Head (mm)		Thickness of Nut (mm)
					Min.	Max.	Approx Across Corners (mm)	Min.	Max.	Min.	Max.
¹⁄₄	6.350	0.787	4.72	17.55	13.21	13.34	15.49	5.33	5.59	6.10	6.35
⁵⁄₁₆	7.938	0.709	6.13	29.55	15.11	15.24	17.53	6.60	6.86	7.67	7.92
³⁄₈	9.525	0.630	7.49	44.06	17.91	18.03	20.83	8.13	8.38	9.27	9.53
⁷⁄₁₆	11.113	0.551	8.79	60.65	20.70	20.83	24.13	9.40	9.65	10.85	11.10
¹⁄₂	12.700	0.472	9.99	78.39	23.24	23.37	26.92	10.92	11.18	12.45	12.70
⁹⁄₁₆	14.288	0.472	11.58	105.29	25.45	25.65	29.72	12.19	12.45	14.02	14.27
⁵⁄₈	15.875	0.433	12.92	131.10	27.74	27.94	32.26	13.72	13.97	15.62	15.88
¹¹⁄₁₆	17.463	0.433	14.51	165.29	30.28	30.48	35.31	14.99	15.24	17.2	17.45
³⁄₄	19.050	0.394	15.80	196.00	32.82	33.02	38.10	16.51	16.76	18.80	19.05
⁷⁄₈	22.225	0.354	18.61	272.00	37.29	37.59	43.43	19.30	19.56	21.97	22.23
1	25.400	0.315	21.33	357.42	42.11	42.42	49.02	22.10	22.35	25.15	25.40
1¹⁄₈	28.575	0.276	23.93	449.61	46.86	47.24	54.61	24.38	24.89	28.07	28.58
1¹⁄₄	31.750	0.276	27.10	576.90	51.69	52.07	60.20	27.18	27.69	31.24	31.75
1³⁄₈	34.925	0.236	29.50	683.68	55.88	56.39	65.02	29.97	30.48	34.42	34.93
1¹⁄₂	38.100	0.236	32.68	838.77	60.71	61.21	70.61	32.77	33.27	37.59	38.10
1⁵⁄₈	41.275	0.197	34.77	949.55	64.90	65.53	75.69	35.56	36.07	40.77	41.28
1³⁄₄	44.450	0.197	37.95	1130.84	69.47	70.10	81.03	38.35	38.86	43.94	44.45
2	50.800	0.177	43.57	1491.03	79.38	80.01	92.46	43.94	44.45	50.29	50.80