I have marked this as "work in progress" as the concept is still under test, any user printing this design please give feedback.
Looking through the options for x-axis belt clamps and tension I decided that none of the designs suited my needs, I did not want to dismantle part of the printer to add a tensioner and clip style tensioners do not offer the same level of adjustment.
So I designed my own, it both clamps the belt and then allows you to tension the belt.
Fit belt in to one block and then attach block loosely to the carriage using appropriate length of screw.
Fit the belt in to the 2nd block ensuring that you take up as much slack on the belt as you can but not so much that you struggle to fit. Again leaving the cross screws slightly loose to allow movement.
Once blocks/belt have been fitted and you are satisfied fit the bolt between the blocks and hand tighten, I squeeze my blocks together and tightened as far as I could. (I would highly recommend that you find a guide on finding the optimum belt tension).
Once your belt is tensioned tighten the four cross screws and happy printing.
Note: Fitting the belt is a bit awkward.
Note 2: you may need to turn your x-axis limit switch to stop it catching on the tensioner block.
I used 100% infill as I thought that would offer the best strength and lower infill din't offer much print time advantage.