Replacement spool core (hub) for https://www.thingiverse.com/thing:3392240 (Fiberlogy refills were a bit too tight for original one).

Screw & nut required, as core is not as tight fit into spool sides as original core.

Print instructions

3 or 4 perimeters, infill isn't critical (10% would be enough)

MMU is not required! Just sliced for MMU2S-single profile.