Printrbot Y Belt Tensioner based off of a design Printrbot use to sell.
This tensioner is slightly different than the one available from Printrbot. You will need a small zip tie and two 1 inch screws with nuts. The fit when printed on my bot is snug enough that the nuts are held in place once pressed in. The follower was designed with nut retention so adjusting the tension will only require a screw driver. Enjoy.