Peter Hirsch posted the folllowing quite a while ago on the Land Rover owners mailing list:
Dear all, in order to contribute something useful for a change I have
compiled a table of spanner (and socket) sizes for the more common metric,
A/F, BSF, Whitworth and BA nuts and bolts.
Please remember:
Metric and A/F bolt and nut sizes are hex sizes, measured between two
opposite flats. BSF an Whitworth are bolt diameters, measured over threads.
God only knows what BA sizes are. The measurements are not the hex sizes,
but the spanner sizes; hexes would be about 0,1 mm smaller (depending on the
state of my tools). Please read all commas as periods, if that makes a
difference to you.
Size Standard Spanner distance in mm
6 BA 4,9
5 ISO 5,1
1/4 A/F 6,35
6 ISO 6,1
4 BA 6,3
7 ISO 7,1
5/16 A/F 8,0
8 ISO 8,1
2 BA 8,3
1/8 WW 8,7
3/16 BSF 8,7
9 ISO 9,1
3/8 A/F 9,6
10 ISO 10,1
0 BA 10,5
11 ISO 11,1
7/16 A/F 11,2
3/16 WW 11,4
1/4 BSF 11,4
12 ISO 12,1
1/2 A/F 12,7
13 ISO 13,1
1/4 WW 13,5
5/16 BSF 13,5
14 ISO 14,1
9/16 A/F 14,3
15 ISO 15,1
5/16 WW 15,3
3/8 BSF 15,3
5/8 A/F 16,0
16 ISO 16,1
17 ISO 17,1
11/16 A/F 17,5
3/8 WW 18,1
7/16 BSF 18,1
18 ISO 18,1
19 ISO 19,1
3/4 A/F 19,2
20 ISO 20,1
13/16 A/F 20,9
7/16 WW 21,0
1/2 BSF 21,0
21 ISO 21,1
22 ISO 22,1
7/8 A/F 22,4
23 ISO 23,1
1/2 WW 23,5
9/16 BSF 23,5
15/16 A/F 24,0
24 ISO 24,1
1 A/F 25,6
9/16 WW 25,8
5/8 BSF 25,8
5/8 WW 28,0
This may help if you can't reach the correct spanner while you are wedged
under the car, so memorize it, please. However, the right tool is the best tool!
Also Dr. Paul S. Crawford of Dundee University sent us this link to his own excellent size/nut table which is very comprehensive:
http://www.sat.dundee.ac.uk/~psc/spanner_jaw.html