Some of the old OS .15's FP? had a 7/32" - 32 thread which is a 12-32. Quite an odd thread. I just bought one for $12 to make one spinner, and then an old neighbor give me a couple hundred taps of every size I could think of. BSW sets, lots of weird stuff. I used a 12-28 tap for a lot of threaded inserts at work with a modified inside diameter. There was little tangs to lock the insert in place. Nice insert for some things.I put thousands of them in. Otherwise it is pretty much not popular.