UPDATE 6/4/17: I uploaded a v2 after the previous version broke due to it being too weak.
Here is a belt tesioner I created to replace the metal spring tensioner that comes with the Monoprice Maker Select v2/ Wanhao Duplicator i3 3d printer. It works great with the thorped cooling mod due to it's small size.
This is a remix of adamstibilj's version from thingiverse. I simply added a slot for an m3 threaded nut so it would thread much more securely.
Hardware required: M3 nyloc (or regular) nut and an m3 screw (I just picked on that was short enough).