customizable filament spool hub for PVC pipe

I appreciate rowokii's customizable spool holder, but wanted something that would work better with PVC than a threaded rod. Since I have a wide range of spool diameters I didn't want a lot of wasted space or distance between spools in my dry boxes, so I adapted a piece of rowokii's model and simplified it.

I'll add more photos over time and work on this further if anyone has comments/suggestions.

In OpenSCAD, here's what you can customize:

- 'diameter' -- this is the diameter of the inn