Designed and printed this spool holder for myself, made it so you can adjust it by the width of the spools.
Fits with ordinary 608( od: 24mm, id: 9mm,W: 8mm ) bearings and the screws i just took some that fit the holes hehe, the holes are 2,5mm so m3 might work fine as they should make their own threads in the plastic then!
Be sure to print the parts with the pins etc pointing up.
And the 4 small stoppers for the bearings must be printed with the convex surface downwards.
They have small risers to press on the center parts of the bearings and those must point up otherwise it might not print so good!
I also used a little short m3 screw from an old computer as the lock screw as you can see in one of the pictures. :)
Works as a charm so get printing now!
And yeah I forgot to mention, the pins for the bearings are slightly shorter then the width of the bearings, and that is to assure good pressure on the center of the bearings.
just use like 15mm screws and it will be no problem :)!