Two skates can be placed under a spool to allow the filament spool to turn. These skates can be placed any distance apart to allow spools of any size to be used. I use it in my Kobra 3 setup to print filaments that are too flexible or rigid to be fed through the ACE unit. 

This design calls for four rollers for which I used these from a local hardware store. Any ~1" sliding door rollers should work.
https://www.doitbest.com/product/235960/prime-line-1-1-4-in-sliding-door-roller-set-2-count-235960/?member=jerrys-hardware

It did require some sanding to get the pins to slide in, but you want it to be a press fit, so that's intentional.

Good luck and happy printing!