(02-07-2023, 06:04 PM)Denis Sweeney Wrote: My understanding was that bolt heads and nuts of both Whitworth and BSF were reduced in size during WW2 in an effort to save on steel. They never returned to the original size.
I have pre war spanner’s that do not fit modern equivalents or some nuts on my Austin whilst the same spanner do fit those that were original.
Almost correct!
It was World War 1 when the sizes were reduced, a 3/16" Whit thread, for example used a nut with a 3/16" Whit hexagon before this. After the change, a 1/4" Whit thread used a 3/16" hexagon. There was a period where the reduction only applied to BSF sizes, hence the dual marking of spanners.
Trying to explain to people who have only ever dealt with metric spanners sizes is challenging!