Filament Spool Adapter with Bearing for 3D printers.

Two of these assemblies fit on either side of a Filament reel. A length of M8 threaded rod slides into the holes in the bearings and rests on the Filament Spool Brackets published here: http://www.thingiverse.com/thing:1565465.
Almost frictionless compared with the original spool holder, eliminating one of the causes of Z-axis issues.
The stepped discs are matched to the sizes of the centre-holes of three common filament spools.

Apart from 2 copies of the end disc and the spool adaptor, y