Spool holder Adapter ring
thingiverse
Adapter ring for Kossel Mini spool holder: https://www.thingiverse.com/thing:454808/ This ring is made for the ~55 mm spools, while the bearing has only ~52 mm. Spools inner hole should be 55 mm, some are a tad larger. The ring avoids play between spool and holder so that it rotates smoothly. The ring is slightly coned, so that it can be easily pressed on the bearing and still has a tight fit, same on the outside. Edit the parameters in the openScad source to adapt it to your needs. You may want to print different Adapter rings for each brand of filament / spool you use.
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