Cylinder Ceiling Thing

Ever need to print a cylindrical hole that changes to a smaller diameter part way up, and need your slicer to do something sensible with it? I found myself needing to do it a lot (screw-holes in the bottom of things for example), so I created this bit of OpenSCAD code (now a customiser) to generate it quickly. It transitions from the wider diameter to the narrower one using two layers that encourage your slicer to do some sensible bridging.

I use it to create an STL, then import it into my mo