This is a simple cam cleat for holding ropes or elastic under tension. Used in pairs, the tension of the rope forces the cleat to close more strongly.

I designed this for a catapult powered by surgical tubing. The cleat allows the tension on the tubing to be adjusted.

Print a pair using tight enough infill for the strength of your application. They are reversed so the teeth mesh and then attached to a surface with screws so the cams can still rotate but not move up and down. For gripping surgical tubing I applied some self-adhesive non-slip material to the inside of the teeth.