Used to hang fixtures. Cover accepts devices with mounting screw centers of 2 3/4" , 3 1/2" , and 4 1/16" [70mm, 89mm, and 103mm]. Base has four holes for fixture studs, four 1/2" trade size KOs, and raised section for no-bolt fixture-stud. Use as a junction or pull box with 5736 Blank Cover. Outside diameter 4 3/4" [121mm].