Just uploaded the updated version with slightly thicker ribs, rounded corners, and easier fit in the center hole.
I designed these rings to fit the cardboard spools for Printbed filament. I got tired of the cardboard dust and wobble that you get from spools with dented edges. The ring snaps into the center of the spool and has 3 teeth that dig in and prevent it from slipping. I have tested it on 8 spools so far without issue. No more errors because the spool slipped and couldn't retract.
Printed in Printbed black PLA on textured PEI plate. Original model was drawn in Fusion 360