bolts, nuts, threaded rods - OpenSCAD library Threading.scad

++last code update 2021.02
++tested to run on OpenSCAD 2021.01

in 2016 I needed some threaded rods and didn't find a good library here. As OpenSCAD is not well enough equipped to do threaded stuff having small slope, I decided to write my own code, using some sweep() functionality I had published earlier with my [Naca_sweep.scad library](http://www.thingiverse.com/thing:900137).

Note: This lib is maintained from time to time - whenever I need threadings with new aspects I expand the code base a bit and adapt it to the newest release of OpenSCAD.