The Yale PM246 2 lever mortice sashlocks offers a standard level of security and are suitable for use on internal timber doors. The deadbolt is locked or unlocked by key from either side. These sashlocks also have a 12.5mm deadbolt, and are suitable for use on internal doors where privacy is required. A deadlock has a single deadbolt which is unlocked and locked by means of a key from either side, whereas, a sashlock has both a deadbolt and a latch which is operated from either side by a lever handles. The security level of mortice deadlocks or sashlocks ranges from 2-5 levers. The higher the number of levers the more secure the lock is. Finish: Polished Chrome Case Size: 80mm x 102mm (3 in) Backset: 57mm This is the measurement from the edge of the door to the centre of the keyhole. Centre: 57mm This is the measurement from the centre of the follower, which operates the handles, to the centre of the keyhole. In the UK this is commonly 57mm.