SOCKETS and WRENCHES (SPANNERS) Key to Nut & Bolt Sizes
Nut size Across Flats			British sizes
decimal in.	mm	in.	BA	BSF	BSW
0.250		1/4
0.276	7
0.282			3
0.312		5/16
0.316	8
0.324			2
0.340				3/16	1/8
0.343		11/32
0.354	9
0.365			1
0.375		3/8
0.394	10
0.412			0
0.433	11
0.437		7/16
0.445				1/4	3/16
0.472	12
0.500		1/2
0.512	13
0.525				5/16	1/4
0.551	14
0.562		9/16
0.590	15
0.600				3/8	5/16
0.625		5/8
0.629	16
0.669	17
0.687		11/16
0.708	18
0.710				7/16	3/8
0.748	19
0.750		3/4
0.787	20
0.812		13/16
0.820				1/2	7/16
0.827	21
0.866	22
0.875		7/8
0.906	23
0.920				9/16	1/2
0.938		15/16
0.945	24
0.984	25
1.000		1
1.010				5/8	9/16
1.024	26
1.063	27	1 1/16
1.100				11/16	5/8
1.102	28
1.125		1 1/8
1.181	30
1.188		1 3/16
1.200				3/4	11/16
1.250		1 1/4
1.260	32
1.300				7/8	3/4
1.313		1 5/16
1.339	34
1.375		1 3/8
1.390					13/16
1.417	36
1.438		1 7/16
1.480				1	7/8
1.496	38
1.500		1 1/2
1.563		1 9/16
1.575	40				15/16
1.625		1 5/8
1.670				1 1/8	1
1.688		1 11/16
1.750		1 3/4
1.811	46
1.813		1 13/16
1.850	47
1.860					1 1/8
1.875		1 7/8
1.890	48
1.938		1 15/16
1.969	50
2.000		2
2.050					1 1/4