The Yale Locks YALPM560CH25 PM560 Hi-Security BS 5 Lever Mortice Sashlock 68mm 2.5 inch comes in the following:
Finish: Polished Chrome
Case Size: 68 x 109.6mm
Backset: 45mm 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.