Spool holder for 30 to 55 mm centerhole spools

Uses two 608ZZ (roller skate) bearings for one side, so total 4 bearings are needed for two cones.
Created one of my own after one spool dropped down on the print head (I have a large delta with spool attached on top of it), causing the print head to lose it's position and a failed print, of course. The reason for this was, because previous holders were slowly "unscrewing" the 8mm threaded rod (used as axis for the holders) - the plastic part was touching the rod, thus creating slight drag.
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