On Feb 15, 10:21*am, "Norm Dresner" wrote:
AFAICT, 8-36 UNF and metric M4x.7 screws and nuts are totally
interchangeable.

Are there any other pairs of metric and US screw threads that can substitute
for one another?

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.