I designed this to fit the Prusa Bear quick release spool holder arm. I use spool holders inside my 3D printer's enclosure, but for certain filaments (like TPU), the spool needs to be mounted on top. 

This slide on spool holder keeps the tabletop clear. 

Previously, I used flat holders, but the spools would occasionally roll over.

You will need 4xM3 screws and 2 608 bearings