The Yale PM560 British Standard 5 lever mortice sashlocks offer a very high level of security and are suitable for use on external timber doors. The deadbolt is locked or unlocked by key from either side with the latchbolt withdrawn by lever handle from either side. The PM560 series locks are recommended by insurance companies, kitemarked to BS3621: 2007 and have been approved by the police Secured by Design initiative. These sashlocks also have a 20mm anti-saw deadbolt, an anti-drill case and are pierced to accept bolt through furniture. A deadlock has a single deadbolt which is locked or 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 Yale Locks YALPM560CH30 PM560 Hi-Security BS 5 Lever Mortice Sashlock 68mm 3 inch comes in the following:Finish: Polished ChromeCase Size: 81mm x 109.6mmBackset: 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.