small discrete universal spool holder. works for everysize spool and is strong enough to easily hold 20kg.
The holder consists of two plates (a lower and a top bearing plate) with races to allow for 5mm (diameter) thick steel balls. there is a spacer/cage for these balls included to keep them spaced properly.
additional a fillement guild could be used, but i found it not needed.
I did use some double sided tape on the underside of the holder to keep it in place, with the vibrations of the printer would sometimes, when the spool is nearly empty, cause it to slide out of position. I did not have any problems with the spool itself sliding off.
used 3 perimeter layers, but can be done with 2, maybe even 1.