EZ Clip-On Filament Guide for Feed Me!

Derived from a great key ring here on Thingiverse, the entire part is designed using the same code, just intersecting to create the necessary structure to capture the filament even without reloading it into your extruder.

Place it over the edge of your Prusa Mendel printer frame (mine is from MakerGear), and it will enable your horizontally mounted filament spool to be evenly pulled by the extruder gear, just like this mount:

http://www.thingiverse.com/thing:123152