REAL (cardboard) Filament-spool adapter

thingiverse

REAL filament often comes on a cardboard spool from the Dutch brand. That's perfectly fine, but most filament spool holders may cause damage and therefore weaken the spool. This ring fits snugly in the spool, making it sturdy and wear-proof. Removing this ring will probably damage the spool, so print a few sets and recycle them when a spool is empty to reuse them.