Filament Spool Joiner

https://www.thingiverse.com/elhalpern did a great job with his https://www.thingiverse.com/thing:4304544 design, but it was created using imperial measurements, which Cura wouldn't convert for me.

I took his design, loaded it into Prusaslicer, converted it to metric, reorientated it to print with the ring down, repaired it with netfabb, and exported it to STL. Now loads into Cura without an issue. No other modifications have been done.

They're joined together by 2 tie wraps.