The moral of all this discussion is to not throw away that can of British Fasteners
we all have on the shelf somewhere . My last BSA , a B50, requires both SAE and Whitworth
tools to work on. I think where they had leftover inventory of parts from the 250 and 441 models they used them up.
I often would replace thru bolted stuff with SAE just to save the Whitworth
for a bike that had to have those threads.