I use this to tension and guide my filament into the extruder from my spindle. I sometimes had problems in which my filament would catch on the inside-corner of the extruder when it was at too great an angle due to my stubborn spindle. This solves the problem perfectly!

This part mounts to http://www.thingiverse.com/thing:3791 with three M3x16 bolts and three M3 nuts.