Free 

Requires: 2 skateboard bearings and a bucket.
Out of the box, it's designed for 608 bearings (22x7mm) and a standard 5-gal shop bucket, but the parametric OpenSCAD file can generate variations of any length and diam, so you can adapt it to whatever you have on hand.
Plus, this version prints in ⅓ the time of the original.
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