My modified version of the belt tensioner that's already posted here. I made one and noticed the pully wasn't completely aligned. Also I wasn't really satisfied with the amount of 'flesh' around the bolt holes.
This design allows you to straighten the pulley out because it is tensioned on two sides.
I used M330 bolts to connect the tensioners to the holder (leftover in the kit). Tensioning is done with M425 bolts.