Found the differences in the angles between the vees.
"MG T Series Handbook" in the article about 'Bolts and Nuts M.G.
Style.' No author is listed but most likely W.K.F. Wood, or Chip
Old.
"On Whitworth fittings, the angle formed by the vee between two
adjacent threads is 55 degrees, while on American National
fittings this angle is 60 degrees. On Whitworth threads, the top
(crest) of each thread and the valley (root) between threads is
rounded off, while on American National threads the crests and
roots are flattened off."
And:
"... the old French Standard metric form differs somewhat from
the modern I.S.O. Standard form. The thread angle is 60 degrees
in both forms, but the thread pitch is sometimes different... a
modern 8 mm bolt normally has a pitch of 1.25 mm, while an 8 mm
French Standard bolt had a pitch of 1 mm."
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