I bought a spool that had a smaller mounting hole than the stock spool holder can hold on my Ender 3, so I made a new one. This uses the original nut and bracket. The post is 65mm long, 13mm thick, and the end is 19mm wide.

I printed it upright on end, with a 0.2mm layer height, supports enabled with an overhang that only adds supports in the screw part (not the sloped section), at least 50% infill, and 6 walls for strength. This might be stronger if printed on it's side, but so far it seems to be working for me. If it fails in a big way I will work on an updated model for more strength.

I also included the screw in case someone wants to use it to design their own holder that uses the stock nut and bracket.

Creality

Ender 3

No

Yes

0.2mm

50%