UL Fire Rated Door Viewer. Used to allow a user to identify visitors from the security of a locked door. UL Listed glass lens. Offers 160 degrees lens angle for wide viewing. Polished brass finish zinc die cast body. Requires a 1/2 inch hole and can be uses in doors that measure 1-3/8 to 2 inch thick. Exterior width is 31/32 inch. Interior width is 9/16 inch. Poly-bagged.