When I was cutting metric threads for Italian bicycle and motorcycle pieces the microcomparator machine said that the original threads were 55deg on every part that I checked. Those were old manufactured parts. There were several metric "standards" in different countries and at some point in time the "new" international metric standards were implemented world-wide. If it's old Italian you'd best get it in a comparator.
The Whitworth (BSW) was 55deg, BSF were indeed 60deg and the BA were 47.5deg.
If you're gonna be cutting any of these you'd best get a copy of Machinery's Handbook and discover just what it is you have before you flip the switch. All of the formulas for dia/pitch/depth are in there.

JIC you don't know about this https://en.wikipedia.org/wiki/Optical_comparator

What Mr. Hebbes says about limiting availability is the essence of British industry. Especially since if it's Brit there is gonna be a LARGE replacement parts market.

have another day
Dr.WtS

Dr.WtS
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