British Standard Whitworth (BSW) Thread angle 55 degrees. Dimensions in inches

Nom Size	TPI	Bolt Max	Bolt Min	Head Thick	Nut Thick
1/4	20	0.525	0.518	0.22	0.250
5/16	18	0.600	0.592	0.27	0.312
3/8	16	0.710	0.702	0.33	0.375
7/16	14	0.820	0.812	0.38	0.437
1/2	12	0.920	0.912	0.44	0.500
9/16	12	1.010	1.000	0.49	0.562
5/8	11	1.200	1.190	0.60	0.687
3/4	10	1.300	1.288	0.66	0.750
7/8	8	1.480	1.468	0.77	0.875
1	8	1.670	1.658	0.88	1.000

British Standard Fine (BSF) Thread angle 55 degrees. Dimensions in inches

Nom Size	TPI	Bolt Max	Bolt Min	Head Thick	Nut Thick
1/4	26	0.455	0.438	0.19	0.200
5/16	22	0.525	0.518	0.22	0.250
3/8	20	0.600	0.592	0.27	0.312
7/16	18	0.710	0.702	0.33	0.375
1/2	16	0.820	0.812	0.38	0.437
9/16	16	0.920	0.912	0.44	0.500
5/8	14	1.010	1.000	0.49	0.562
3/4	12	1.200	1.190	0.60	0.687
7/8	11	1.300	1.288	0.66	0.750
1	10	1.480	1.468	0.77	0.875
Note that hex sizes are as for BSW but one size smaller.

British standard Cycle (BSC, sometimes BSCY) Thread angle 60 degrees. Dimensions in inches.

Nom Size	TPI	Bolt Max	Bolt Min	Head Thick	Nut Thick
1/4	26
5/16	26
3/8	26
7/16	26
1/2	26/20
9/16	26/20
5/8	26/20
3/4	26/20
7/8	26/20
Notes 1. Alternative 20 TPI for 1/2 inch or bigger. 2. Thread angle 60 not 55 degrees. 3. 1/4 inch BSCY has same TPI as 1/4 BSF and despite difference in thread angle they are virtually interchangeable. 4. Head/Nut sizes as for BSF. 5. There are smaller sizes but in most small BritBike applications, BA fasteners are used.

British Association (BA) to British Standard BS 93. Thread angle 47.5 degrees

BA No.(#)	Diameter mm	Diameter inch	Pitch mm	Pitch inch	TPI (approx)	Hex A/F inch
0	6	0.2362	1.00	0.03937	25.4	0.413
1	5	0.2087	0.90	0.03543	28.2	0.365
2	4.7	0.1850	0.81	0.03189	31.4	0.324
3	4.1	0.1614	0.73	0.02874	34.8	0.282
4	3.6	0.1417	0.66	0.02598	38.5	0.248
5	3.2	0.1260	0.59	0.02322	43.1	0.220
6	2.8	0.1102	0.53	0.02087	47.9	0.193
7	2.5	0.0984	0.48	0.01890	52.9	0.172
8	2.2	0.0866	0.43	0.01693	59.1	0.152
9	1.9	0.0748	0.39	0.01536	65.1	0.131
10	1.7	0.0699	0.35	0.01378	72.6	0.117
Notes: 1. Used for petrol unions on BritBikes. 2. Most Common Sizes 1/4 and 3/8 inch. 3. Use BSW spanner sizes.