The Cardellini Head-Lock is a quick release tie-down for Mitchell base heads. It eliminates the separate knob with a 3/8" stud for securing the head. Instead, the Head-Lock mounts to and stays on, the bottom of the head using a 3/8-16 bolt. When the head is place on the dolly or tripod, the Head-Lock passes through the center of the Mitchell mount. Turning the built in knob from below locks the head in place. There is no more fishing around trying to get the tie-down screw started.