The original prusa filament holder, holds the spool at 2 small cylinders. If you put these too tight you gain friction on the spool. If it's too loose, there is a risk of falling off.

The risk is maybe small, but I still wasn't convinced about their solution so I've made a small axes with a lock, which prevent the spool falling off.

Looks nice, works good, only I had to print this horizontal because of sticky issues with tall objects. I didn't try printing it vertical.

The beard comb is from ShipWreckedMonkey ! https://www.thingiverse.com/thing:1785320