Abstract: A clamp apparatus having a locking body with a tapered lower cam surface, and a stationary mounting member on which the locking body is rotatably mounted. The cam surface is substantially perpendicular to the rotational axis of the locking body to provide a large cam surface area for secure locking and holding of workpieces. A cutout portion on the locking body defines an open position wherein a workpiece can be positioned adjacent to or removed from the clamp apparatus. When the locking body is rotated into a locking position, the tapered cam surface engages and clamps the workpiece beneath the locking body to secure the workpiece in place. A stop or stops on the mounting member prevents the locking body from rotatably moving into unwanted positions. A resilient O-ring positioned between the mounting member and locking body provides traction therebetween.