Find a library. OpenSCAD bundles MCAD, and it has screws. https://github.com/openscad/MCAD/blob/master/screw.scad BOSL2 also has screws. https://github.com/revarbat/BOSL2/wiki/screws.scad There's also a number of Google hits. https://www.google.com/search?q=openscad+screw