RepRapGuru Y-Axis Tensioner

Simple Y-Axis belt tensioner that uses a hex head M5 bolt and M5 nut. The knob makes it much easier to adjust without using any tools.

Heavily inspired by this http://www.thingiverse.com/thing:320268 but redesigned from scratch to use M5 hardware and fit my RepRapGuru i3. Any printer using 8mm threaded rod for the base should work.