Flexibility of traffic control and easy installation is offered by 4900 Series Heavy Duty Deadlatches. A key-controlled bolt hold-back feature allows for two-way traffic for applications which require free entrance at certain times and exit-only at other times. This allows a "locked" entrance to be used as an exit by visitors already in the building. 1-3/4" [44.5 mm] minimum door thickness required. Interchangeable, without stile modification, with any MS1850S deadbolt of same backset and faceplate shape. Also retrofits to existing 4510 and discontinued 4700 Deadlatch preparations.