I had cause recently to want to know the thread pitch on the stem of an Elgin wristwatch I was working on as I was unable to find a crown or stem extension to fit. I tried several different things before hitting upon this idea: A bit of thin soft metal is drilled about .1 mm smaller than the thread. (I used a scrap of copper because that's what I had handy, brass, aluminum or even plastic would probably work as well). Then with the stem held in the headstock of my lathe I carefully turn it while pressing the copper sheet, and the steel threads will self-tap into the soft metal. Once it's started I setup a dial indicator with it's tip as close as possible to the hole (see photo), and carefully measure 10 turns of the headstock. If I wanted to be even more clever I would have taken the time to make a hollow tip for my dial indicator. That would distribute the pressure evenly and make it a bit easier to get an accurate reading. View attachment 4971 In this particular case the 10 turns took 0.083" --> 0.211 mm/turn which is a lot finer than the standard 0.25 mm for a 1mm screw. That also works out to 120 threads/inch, which given this is a American made watch should not be too surprising.