Do you not have a 'Thread Pitch Gauge' ? The difference between 24tpi and 1mm is palpable with well made sets. If you have one such as shown in the referenced Video then maybe not as much
The easy way - though not fool-proof - would be to see whether the thread-form had a rounded or flat crest/root. A Whitworth Form (55°) will (if fully formed) have a rounded crest and root - but if the OD was reduced then it could have a flat. The UNC (60°) could have a rounded root but will always have a flat crest -- as long as it hasn't been worn. So much depends upon how and where it has been used.
pm sent.The easy way - though not fool-proof - would be to see whether the thread-form had a rounded or flat crest/root. A Whitworth Form (55°) will (if fully formed) have a rounded crest and root - but if the OD was reduced then it could have a flat. The UNC (60°) could have a rounded root but will always have a flat crest -- as long as it hasn't been worn. So much depends upon how and where it has been used.
A good quality Thread Pitch Gauge will have both Whit. , Unified and Metric thread form gauges as separate 'leaves' -- the one shown in the video (as explained by the presenter) appears to have Imperial (TPI) legends on one side of each leaf and Metric (Pitch) legends on the other. If that is so, then the thread angle will probably be neither 55° or 60° so would only be useful to check an approximation of the TPI or Pitch, not to determine Whit. , Unified or Metric. I can't point you to a supplier of quality gauges though.
The best way would be to get access to a 50:1 shadowgraph so that you can measure the image
I'm in the process of writing a computer program that calculates the micrometer reading over 'three wires' when measuring the effective diameter of many threads. It also shows the form and various other features which might be useful. If you would like to see (test) a copy send me a PM with your e-mail address.
Very Droll as Sir Humphrey would say!, you seem to have a Thorney issue here, unfortunately I don't have a metal working lathe either, something I have often regretted, but you can't afford everything for your workshop, I have had success in the past making my own bits and pieces using a drill mounted horizontally and a good file to reduce the diameter, then re-threading with a suitable Die, so I think in the absence of suitable machine tool I would try the same, I have also do this with a spinning workpiece against a bench grinder with a finer grit wheel as the other correspondent suggested, I hope this helps
Julie
I / we are almost convinced it is number 12 UNC. tpi definitely 24. OD of threads (digital micro's 'change') but I'd be happier agreeing to 5.486 (#12) rather than 5.556 (BSW 7/32... but 'in brackets possibly OOD or something)
Grinder, with bar in hand held drill?I have had success in the past making my own bits and pieces using a drill mounted horizontally and a good file to reduce the diameter, then re-threading with a suitable Die, so I think in the absence of suitable machine tool I would try the same, I have also do this with a spinning workpiece against a bench grinder with a finer grit wheel as the other correspondent suggested, I hope this helps
I'm somewhat surprised at that, Tracy are usually very good but I've just checked a number of suppliers and even my (normally) trusty Machinery's Handbook and can find very little information on Thread size - Die-Stock size combinations. From experience, I would expect a 7/32" or #12 die to come as a 13/16 OD but that's not guaranteed.
