Designing a spool holder for your 3D printer is probably a right of passage. This is my 3rd, and by far the one I'm happiest with.

Materials:

• 4x 608 skateboard bearings
• 8x 3/8" nuts
• 2x 3/8" threaded rod roughly 6.125" (155mm) in length each

Instructions:

• Print two of the rollers
• Print two of the sides
• Press fit some 608 skateboard bearings into the circular holes in the sides
• Press fit a 3/8" nut into each end of the rollers
• Thread the threaded rod through the nuts in the rollers until there is an equal length protruding from each end
• Place the roller assemblies between the sides with the rods in the inner bearing holes
• Thread the remaining nuts on to each end of the threaded rods, tighten.

I also included a shim.stl file that I used to build up the inner diameter of the bearings I'm using (I found some Peer 7R6 bearings for cheap at a local surplus store). You won't need them if you're using standard 608 bearings.