Not sure if anyone else will find this useful, but after printing the Ender 3 Spool Holder Sidemount by Adrenalinez (https://www.thingiverse.com/thing:3564351) I decided to mount it upside down on the printer's frame to solve a clearance issue. This put the spool a bit closer to the motors than I would like and it was getting caught on them when the spool drifted to the end of the holder. To solve this, I printed this part to force the spool to sit towards one end of the roller and to help prevent spools with large holes in them from coming off the end.
It's designed to take a small #4-40 x 3/4in machine screw and matching nut. The hole is sized so that you can press the nut in or melt it in for a solid fit.

Creality

Ender 3 Pro

No

Yes

0.2

50% (Triangle)

Infill type is entirely optional, I used 50% to make the part stronger so that I could clamp it on tighter and use it as a handle to remove the spool holder when changing filament rolls.