The yale 91 basic nightlatch security lock is key operated from the outside and lever handle operated from the inside on closing the door the snib function bolt hold back button enables the latch to be held back this lock is non deadlocking and is ideal for use in hotels supplied with 1109 cylinder the 91 basic nightlatch has a 60mm backset this is the measurement from the edge of the door to the centre of the keyhole locks with a 40mm backset are normally used where there is restricted space su