The 4510 Series Standard Duty Deadlatch offers flexibility of traffic control during and after business hours. A reverse turn of the key while the bolt is held retracted retains the bolt to allow two-way traffic for healthcare, financial institutions, retail, and other applications that require free entrance at certain times and exit-only at other times. Interchangeable, without stile modification, with any MS1850S Deadlock of same backset and faceplate shape. They do not, however, provide the same maximum security level as the MS Deadlock. Turn key or operate handle or paddle to retract spring-loaded latchbolt. To holdbolt retracted, push it in and secure by reverse turn of key. Lock accepts any standard mortise cylinder with MS cam, available separately. 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 4066Thumbturn, available separately. Lock accepts cylinder from either or both sides.