OpenSCAD Screw Holes

WARNING: I have no 3D printer - this module still needs tuning based upon experiments.
Any help with this will be appreciated.

This provides a module to drill holes for screws.

Usage:


include <screw_holes.scad>
 
difference()
{
solid_object();
// Drill a hole for a DIN965 M3 screw of length 20 mm,
// with 10 mm thread.
screw_hole(DIN965, M3, 20, 10);

// Drill a M4 hole through the 30 mm thick object, with a countersunk
// head with a 90 degree angle that