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. Turn key or operate handle or paddle to retract spring-loaded latchbolt. To hold bolt retracted, push it in and secure by reverse turn of key. Interchangeable, without stile modification, with any MS1850S deadbolt of same backset and faceplate shape. Also retrofits to existing 4510 and discontinued 4700 Deadlatch preparations. Lock accepts any standard 1" [25.4 mm] length, 1-5/32" [29.4 mm] diameter mortise cylinder with MS cam such as the 4036 Mortise Cylinder or thumbturn such as the 4066 Thumbturn, available separately. Lock accepts cylinder from either or both sides.