I wanted a tensioner that would attach to the bed using the supplied two screws and that was easy to mount and which would enable tightening of the belt without tools and without risk of damaging the belt, as with some of the tensioners where the belt is tensioned with a screw directly on the belt or where the belt has to turn a sharp corner.
Also I wanted the thing not to be too large or require too much ABS.
Added an STL for a T2.5 belt - I have not tested this, so please report any misbehavior.
Print the three parts.
Remove the mounting screws from the bed with the previous mount.
Place the base (green part) on the under-side of the bed with the rectangular tab facing away from you.
Thread the screws through the holes in the bed from above as before and through the holes in the base.
Grab the nobbly side of the belt with the nobbly side of the grabber (orange part) and slot the belt and grabber into the groove in the lid (Blue Part) with the smooth side of the belt against the long side of the groove.
Press the lid against the base and tighten the screws into the lid (Nuts should not even be necessary).
Insert and tighten an M4x40 or 50 mm into the grabber and keep tightening until your belt is taut.
- And you will have no more round holes come out as strange ovals :-)