I know there are hundreds of these on here but I designed my own so I could use some spare 608 skate bearings I had in my tool box. Print 2 of these stepped spool holders and press fit 2 608 bearings, one either side, then mount them on an 8mm threaded bar and lock in place with some nuts.

The spool holder is designed to fit anything from 36mm spool hole diameter up. The outer diameter of the holder is 60mm.