4" Round Ceiling Box with two captive mounting screws and four Auto/Clamps. Constructed of impact-resisitant Noryl thermoplastic, making it virtually unbreakable and non-conductive. Auto/Clamp cable clamps molded in, hold wire securly in box. UL Listed for fixture support -- max weight rating 50 lbs. Depth-mounting gauge at bottom of bracket helps you align the box at the proper depth relative to the ceiling.