Parametric spool hub with three spokes and an M8 threaded center hole. Any M8*20mm bolt will fit into this hub and stick out just enough to go into the center of a 608 bearing.

I run some of my filament boxes on axles made from lengths of ground 8mm stainless shaft, but bolts are way cheaper and easier to get hold of.

STLs included:
55mm: Bambu reusable spools, and newer SunLu ones.
54mm: eSun, Jayo, DeepLee.
63mm: older SunLu reusable spools.

Make sure of your own spool dimensions before printing! Sometimes manufacturers change their sizing. If you need a custom size, the .f3d file has a 'spool_ID' parameter; alter that and everything else is taken care of including the de-bossed text label.