The 4-1/2" Grip Head, KG400512 consists of a pair of rotating aluminum discs attached to a junior 1-1/8 (28mm) stud and receiver. The discs have two different sized "V" shaped jaws to accept any accessory with a 5/8" or 3/8" mounting stud or tubing. The "V" shaped jaws have "teeth" that grab whatever is mounted between the plates securely.