Zoo Hardware FB3041CFB Porcelain Door Knob
Facetted mortice door knob
When fitting a door knob where knuckles may scrape on the door frame, fit a longer lock or latch to allow more clearance when turning the knob.
We recommend you fit a lock or latch that's at least 76mm long or 3" Lock.
The length of the lock or latch determines the distance of the door knob from the edge of the door frame:
e.g a 64mm or 2.5 inch lock/latch will only give a backset of 45mm, a 76mm or 3 inch lock/latch has a backset of 57mm. This means that the centre of your chosen door knob will sit 57mm in from the edge of the door.