I have a few Victorian era lenses (1860~1900) and need to have some mounting flanges made. Is there any resource which specifies the threads used by the various manufacturers? I can measure the outer diameter of the threads easily enough and will get a thread gauge to work out tpi, but what of the thread angle? Was 60 degrees used as a 'standard' before ~1900? if not what other threads were used. I query if there was any standardisation because I have items with threads from different manufacturers, and at least a couple of decades apart, which seem to be the same so it would be really useful to know specifics to discuss my needs with the machinist who will make the flanges.