I have a Prusa i1, and all the spool holders I could find have different measurements between top shafts or other issues. This is designed for 8mm rods, spaced 57mm centres. I have designed this to work for Vik's diamondage 125m Spools, based on 200mm full, and 90mm empty, the filament should not touch threaded rods, using Vik's spool holder and ABEC-9 skate bearings, super smooth filament feed is the goal. I drilled the centre of Vik's spool holders out to Ø14mm as the inner race was touching, providing some drag to the holder.

print, position spool above printhead, print better.

Revised, spool now sits 60mm further to the back, as testing indicated this is required (white arms in photograph).

Finished print (yellow arms in photograph) now working as expected!

(even though it looks a bit like its touching in the photo, the filament travels neatly in the middle of the two threaded rods, with no interference anywhere