This is a simple, one-piece part to mount a filament spool on top of a Kossel or a similar delta printer. This particular mount was made for a spool with a 45 mm hub, but a similar one can be made for other hub sizes easily.
Use two 8mm M3 screws and m3 nuts to mount the part on the top side of the printer.
No bearings or other moving parts are needed - the spool just slides with very little friction.
This configuration is surprisingly stable - the printer is very far from tipping over with a typical 1kg spool.