"Andy Champ" wrote in message
...
....
"I think you will find that 1/4" BSW (British Standard Whitworth) is
close enough to 1/4-20 UNC (Unified National Coarse) to be considered
interchangeable for non-critical applications such as this (if this
were an airplane, I'd think differently). The differences are out in
the third decimal place, being on the order of 0.005" or less...

That was rather the point of the Unified thread - to provide something that
would work with both British and US standard threads, to improve
interchangability between allies during the war. They were, incidentally,
used in some aircraft equipment although, according to my late father who
was an aircraft instrument fitter, where the British aircraft were designed
so that you could dismantle anything with a standard toolkit, the Americans
would design the aircraft first, then a set of specialised tools you needed
to get to the fixings they had put behind things.

Colin Bignell