This spool holder is meant to be a very simple and straight forward design. I only use ColorFabb, so all of my spools are of the 55mm variety.  I've used and printed a variety of spool holders and have tried to incorporate what i want and actually need. The rounded inner edges keep the spool from catching on the sides, the bearings provide the smoothest feed you can possibly get, and its small footprint and design provides a strong but low filament expense when printing.

Tip: I used a measured piece of plastic pvc tubing to act as a stop for the bearings, but you can substitute this material with anything you'd like such as lock nuts or even maybe zip ties. Just slide everything along the bolt while threading it on.

Printing: .80 Wall Thickness, 20% infill.