Belt tensioner for GT2 belts.
Strongly based on ThomasKTN Belt shortener for Ultimaker, it features a clip to lock the main part and press the belt tightly.
It uses a DIN912 M3x35 bolt and one M3 nut.
Print a pair of each piece, place the screw, fit the belt and lock with the clip.
I added the .skp of the clip, so you can make little adjustments if your printed part requires so.
EDIT: Added inverted part, where teeth are on the opposite side, so it can fit in different positions in the printer housing.
EDIT: Added GT2-10mm belt body version (provisional)