Parametric Post Cap Adapter

I wanted to install some solar-powered lights on the posts of my deck. Those posts are (nominally) 3.5 inches on a side, and the lights I wanted to use are for posts that are (nominally) 4 inches on a side. Because of the way lumber is sold in the US, those are not the actual measurements of either. But, the point is, I needed something to cover the gap between the post and the mounts for the lights. Besides bridging that gap for stability, the adapter also gives the mounting screws a bit more to bite into when you consider the bevels at the top of a typical wooden post.

I knew I would have to do some experimental "dialing it in" until I got the right dimensions, so I did the design in OpenSCAD with all the dimensions being parameters. You are likely to find some small variations in the actual post sizes, and you will have some percentage of shrinkage in the 3D printing filament. To experiment with sizes, I printed sections that were vertically very short. I could print them in 20-3