Prusa i3 spool holder for Bowden extruder

Preparing my Prusa i3 for dual extruder setup. And therefore also holder for two spools. Sit on top of frame. The screw holes is for Compact Bowden Extruder, direct drive 1.75mm (http://www.thingiverse.com/thing:275593) and using also 4 pcs. of Universal Spool Holder 18-56mm II, 606ZZ/608ZZ with 608ZZ bearring. (http://www.thingiverse.com/thing:124649)