This is a low investment (only about 60g each side) master spool scaled for polymaker refill spools. For me these came out as press-fit into the cardboard.
I thought this design was pretty so I used it as a base despite the fact that the sticker from polymaker has no spot on it. If someone wants to remix this with a view window and a space for the sticker that'd be great!
No support needed, just print 2 of these and press them into each side of the refill spool.
I used PETG in case I need to dry out any of the spools later. PLA can sag if put in a heat-based filament dryer.
EDIT: As I've made a few of these, 2 out of the 10 spools I've used were too loose for a press fit. I put some blue tape on the inside of the cardboard as filler and that worked great.
The author remixed this model.
Scaled for Polymaker Refill spools and bumped out the outer diameter. Also added more filament holes along the edge.