Published my 3D-design of a filament spool holder for M8 threaded rod:
thingiverse.com/thing:6720933
We're actively using this design in our local hackerspace and it turned out to be quite practical.
Made with @FreeCAD, of course. 
#freecad #3dprinting #accessories
Filamend Spool Holder (for M8 threaded rod) by a_v_p
This is a filament spool holder for a M8 threaded rod.You also need the following components:1 M8 nut for each "M8-nut-knob".1 608zz bearing for each "filament-spool-holder".Thingiverse