This baby 5/8" (16mm) stud quickly attaches to any of the mounting locations on either the 3 Way Clamp (KG900412) or 4 Way Clamp (KG900712) to accept any light fixture or accessory with a baby 5/8" (16mm) receiver. All accessories for the 3 and 4 Way Clamp System have a proprietary notch that slides into one of the mounting locations and then is secured by turning the locking collar. It is 2.6" (66mm) long.