A camming clamp has a fixed jaw, a pair anchored in the fixed jaw, and a moving jaw threaded onto the guides. A levered cam is threaded onto at least one guide. A backing surface is threaded onto the same one guide. It sandwiches the levered cam between itself and the moving jaw. An adjustable locking provision locks the backing surface at fixed positions along this guide with the levered cam. Wherein, the levered cam has a cam head with an over-center axis such that, when rolled on one side of the over-center axis the camming clamp is slack and adapted to position the jaws on opposite sides of an object to be clamped, and, when rolled over the other side of the over-center axis the jaws clamp tight on said object. The over-center axis prevents the cam head from auto-pivoting back to slack.