ISO/UTS thread OpenSCAD library

Making a simple thread in openSCAD is easy - linear_extrude an offset circle with a twist - and that works quite well. However you have to use a lot of slices to avoid some strange effects on the twisted extrude, and you end up with a sign wave thread cross section which is unconventional.

As such I have been playing with making a proper ISO/UTS thread without too many faces. It took me several attempts to get this right - do leave comments.

It is designed for metric, but the shape is the same for UTS, so you can use the library, specifying the thread pitch you need, to make UTS.

I've added the OpenSCAD - written to work as a library allowing nut, bolt, or arbitrary sections of thread - have fun.

P.S. I have looked through a load of the other thread libraries on here - I think I am the only one that has constructed it in this way - some interesting different approaches to the same problem though. Fun.