It's a 2 part spool holder. The design is made to match with 2020 extrusion profile. I used 605Z bearings for this. The bearings are held with M5 screws. For mounting I used M3 screws but anything will work I guess.

I printed this with SUNLU PLA+ with 1.6mm walls and 10% infill. Not the best setting but it was strong enough and held 1kg spool without any deformation.