PM320 3 Lever Mortice Sashlock Polished Chrome 79mm 3in
Finish: Polished Chrome Case Size: 79mm x 101mm (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.