Printrbot Jr Y Axis Belt Tensioner

I crafted this replacement for the Printrbot Jr's y-axis end cap to include a belt tensioner after being inspired by things http://www.thingiverse.com/thing:10274 and http://www.thingiverse.com/thing:13479.

The .stl file is an export of the .scad file configured for 6-32 screws and nuts, but feel free to fiddle with the parameters to customize it if necessary.