came across this site detailing jaw openings for various "standard nuts", you often see thread tables but not many of these. Interesting.
also the observation there "It is a common view that the odd Whitworth/BS spanner sizes are 'illogical' and that the newer metric system is much more 'logical', but consider this: To cover 1/4" to 3/4" in both fine (BSF) and coarse (BSW) threads, the British system defines 9 diameters and requires 9 spanners (or 10 if you also include the original large head Whitworth sizes as well). The UNF/UNC system defines 8 diameters for the same range but requires 11 spanners. For the broadly equivalent range in metric of M6 to M18 using all the common metric standards in use, there are 8 diameters defined but a total of 15 spanners are required! (i.e. 69% more spanners per diameters than the British system). Is this progress?"