Prusa I3 Y Belt tensioner

*Updated: Changed the nut retainer on the pulley side to fit a M4 nut. Added a slot to fit an internal M3 nut instead of using one on the inside where the rods go. Designed to use these bearings / adapter: http://www.thingiverse.com/thing:98787

I here a mashup of a few parts to make a Y belt tensioner for a Prusa I3 I am making. I wasn't happy with a couple I downloaded. Uses a M3 screw and fits 5/16" rods. I also resized the bearing screw hole for an M4 since I am using a belt bearing pulle