Yeah Trev,
I've done a lot of that too, and don't want to split hairs, but it's worth keeping in mind that a lot of bolts that are sold as Whitworth, are actually UNC, in most cases doesn't matter, but when the thread form is important, it does matter.....WW=55˚/UNC=60˚
The way I see it, it's not a true Whitworth (bolt)unless it takes a Whitworth spanner- eg; WW 5/16" bolt =1/4"ww spanner, UNC 5/16"= 1/2" spanner (A/F)...am I wrong.??
cheers, duTch