Identical Metric and US Screw Threads

Not metric, but UNC threads of 3/16"(10-24) and above are identical to Whitworth apart from the thread form with the notable exception of 1/2". This leads to the confusion that some people think that 1/4" and 3/8" camera tripod threads are UNC (they aren't, they have always been Whitworth).

regards Mark Rand RTFM

I frequently confuse M5x.8 with 10-32 - 5mm is roughly .197 inch and .8 pitch is 31.75 TPI.

Steve

Yep, I've seen gear clusters on a bicycle with either 1 mm (25.4 tpi) or 24 threads per inch, and either will fit any hub.

It doesn't work out well at ALL, though: the mismatched threads result in a six-thread fit having two in tension, two out of contact, and two in compression. The two in tension fail (because the compression plus the load is too much force), then it's one thread in tension, two out of contact, and one in compression... which also fails.

Most bicycle shops are aware of the problem, and have thread gages. Even I learned the lesson, after buying a few hubs.

The hub issue is less than 1% mismatch, and your example of 8-36 and M4x.7 is (nominally, in thread pitch) similar. It might work if the materials stretch enough without fracturing, but it'd be nice not to depend on that.

|Yep, I've seen gear clusters on a bicycle with either 1 mm (25.4 tpi) |or 24 threads per inch, and either will fit any hub. | |The hub issue is less than 1% mismatch, and your example |of 8-36 and M4x.7 is (nominally, in thread pitch) similar. It might| work if the materials stretch enough without fracturing, but |it'd be nice not to depend on that.

The 8-36 and M4x.7 are 0.8% apart and, at least for the 1/2" or so that I need, are, if my calculation is correct, about .0001" different after the .5" interval which, I don't think should matter that much for most things.

Norm