This clamp is made from Vice-Grip welders clamping pliers. The lower jaw extension has has been removed and replaced by a square bar that fits in the anvil's hardy hole. The sample above was designed to take a wedge that was later found unnecessary. To operate all you do is drop the shank into the hardy hole and over a piece of work, then clamp. The loose fitting shank cocks just enough to lock in the anvil.