12-09-2016, 08:26 PM
The problem with trying to get a metric/UN fit is that the you need to ensure that the threads are short. As Ed pointed out, 20tpi and 1.25 pitch are extremely close and one of the short thread gauges will fit both nicely. The only way to distinguish between the two is with a ruler. You need to measure the crest over a one inch length. Only the 20tpi thread will have a crest that lines up with the zero and the one.
If you are making mating parts then I wouldn't worry about trying to make a metric thread. Just pick a thread that works for your application (i.e. coarse or fine) and have at it. If you are making something to fit existing parts, then that is where you will have to take Vinny's advice. Of course, you can make (or get made locally) any gear you need. You don't have to send off to the U.S. for one.
The thread you cut looks very nice although somewhat shallow. Measure the number of crests over one inch and check that number corresponds to the settings on your gearbox.
If you are making mating parts then I wouldn't worry about trying to make a metric thread. Just pick a thread that works for your application (i.e. coarse or fine) and have at it. If you are making something to fit existing parts, then that is where you will have to take Vinny's advice. Of course, you can make (or get made locally) any gear you need. You don't have to send off to the U.S. for one.
The thread you cut looks very nice although somewhat shallow. Measure the number of crests over one inch and check that number corresponds to the settings on your gearbox.
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