Pivot-Lever One-Piece Gripping One-Screw Tensioner
Scableable belt tensioner works with a range of belt sizes, in multiple orientations and belt positions.
Sawtooth teeth on both sides of channel help grip the belt (belt can be installed with teeth facing in or out). As tension increases on the belt, it pulls the flexible arm into the larger fixed arm, pinching the belt for even better grip.
ABS is probably better than PLA as the flexibility will help it grip the belt better.
Requires only one screw, one nut, and one cable tie.