The Manfrotto 595CLA Fig Rig Clamp is part of the 595B Fig Rig Camera Stabilizer. It consists of a camera platform with a threaded screw bolt, similar to Bogen's #577. The screw bolt has both standard 1/4-20 and 3/8" threads for mounting to the bottom of your camera. A bottom post locks the clamp into place, and acts as an additional handle.

Manfrotto 595CLA Fig Rig Clamp Locking Post