When I built my 3D printer, I mounted a short length of 3/4" electrical conduit for hanging filament reels. While every filament reel I've hung from it fits, they're usually too loose—flopping around during printing and creating unnecessary resistance.
To remedy this problem, I made this universal spool adapter. It fits a wide variety of spool sizes, and has an inner diameter of 2 cm, except at the ends, where it widens to 22 mm to allowing for the fitting of 608zz bearings. It screws together easily, automatically centering itself in the hub of the spool.
Designed using PTC Creo in August, 2017. Refer to its Thingiverse page for downloads and more information. There, you'll two versions, the original, and one with an additional 4 cm of length for wider spools.
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