Screw Threads, Holes, Bolts, Nuts, and Rods Library

This was my first 3D printing design. I decided to try to make a convenient OpenSCAD threading library, since I figured I would use it in many other designs. It expanded a little as I was developing it, and it now supports metric compatible internal and external threads, auger threads, thread tapering, clearance holes, countersunk holes, recessed holes, hex bolts, nuts, washers, and long rods which are extended with threaded joints. Whenever possible I attempted to comply with metric standards for the defaults of parameters, while providing overrides for many values.

...........
Version 2 updates (2017-03-20):

For version 2, I redesigned the core threading routine to use list comprehension to generate the entire threaded screw as a single polyhedron. This substantially improved the rendering speed and robustness, decreased the number of facets necessary, and increased the tactile smoothness of the resulting parts. I also added auger-style threading, partially tapered screw ends, auger and conventional threads which come to a point, and support for Phillips tips.

Version 2.1 (2017-04-10) fixes an error in the declaration of auger thread angles.
...........

Since this is primarily a library for use in other designs, I will briefly list the API here. Where parameters are shown with a default of 0 or -1, in many cases this indicates a standard default value will be calculated internally if this is not overridden.

~~~
// This creates a vertical rod at the…