A more symmetrical version of Athorbot Spool Holder by DrStreet . I have included 2 roller designs. Originally I made the roller with a hollowed out core thinking that this would save printing time and material. Because of the larger inner diameter this actually takes longer to print than the stright 8.5mm bore, but it might provide more strength where the spool rests.
Playing around in Cura, the hollowed out one might take 2¼ hours and 3.92m of PLA. The straight version a little under 2 hours and 4.04m. So technically the hollowed out one does use less material. I left the hollowed version in out of interest. The graphic shows the difference in cross section with the straight version on the left and hollowed to the right. If I were printing this again I would use the straight, but since I printed the hollowed first and it worked. Consequently I have not tested the straight bore roller file.
The spool roller is 50mm⌀ with an 8.5mm bore, so good for an M8 threaded rod. It is fixed to the Athorbot frame by 4x M4 12mm bolts that I happened to have spare.
Following a suggestion from the original designer I added another version of the tower with a cut out so that the spool holder can be lifted out rather than completely unthreaded, this should make changing filament quicker, and is reported to work (thanks BuggZy).