This is a shim that I designed to reduce the hole size of a spool of filament I bought that had a 73mm hole diameter. My spool holder couldn't firmly hold a spool with a hole diameter greater than about 60mm, so I designed this shim to fit inside. I made mine JUST small enough to fit inside and pounded it gently in with a rubber mallet for a nice firm grip. The ends are chamfered to make that process easier. I made mine out of PLA, but a slightly more pliable material might be preferable.
Since I figure there could be other sizes people needed, I tried to make a .scad file, but I've never made one before, so here's hoping it works! Suggestions are welcome!