Filament on top of my kossel was a bit wobbly while printing, so i made these inserts to make the movement smoother.

I use this filament holder:
https://www.thingiverse.com/thing:2476209
Might work with others also, let me know in the comments.

Tight one is about 19mm on the inside, regular is about 22mm.
V1 is about 52.8mm and fits great on spools from "Clas Ohlson"
V2 and V3 fits random spools from china. just mesure first.

1-2% infill should be enought if it is spread even.