Summary

A simple tube for spool holders

Should reduce friction
Work cleaner than some spool holders without this addon (like original on Voron0, using cardboard spools was messy)

Tested on Ender 3 and Voron0

IMPORTANT
Measure how big the hole needs to be.
Like on Ender 3 spool holder there is a big rim on the end, you need to make the print bigger than that, not only bigger than the size in the middle
Model for other spool holders than for Ender 3 and Voron 0 is with 100x100mm size for easier resizing
If you need a 70mm long tube with 40mm diameter just print the model with 70% size on Z axis and 40% on X and Y

Print in Vase Mode (Spiralize Outer Contour)
NO bottom layers (nor top ones)
You can use brim on print but be carefull with removing it

Material shouldn't matter much. I think I printed both with PLA