In article ,
David wrote:
Most people seem to class American Forces (AF) sizes as Imperial.

AF on a spanner refers to the Across Flats size in inches.

During WW2 unified threads were agreed so things could be produced in both
the US and UK. Although more based on the original American Fine threads
than UK ones. And used by much of the UK car industry until metrication in
the '70s.

Now
there may be a hint in the name, but I didn't think that (officially)
the USA was classed as an Imperial power. Certainly not by the UK in the
1950s/1960s when AF sizes were more common. I think they may be classed
as Unified though.

Imperial to me would be the various Whitworth threads and heads,
including British Standard Fine (BSF).

Yes - my first socket set which had BSW/BSF and AF sizes said Imperial and
Unified.

--
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Dave Plowman London SW
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