DOOR HARDWARE - Doorsets - Function & Backset
QUESTION: How do I determine which function I need for my door set?
ANSWER: There a 4 basic functions for conversion/tubular doorsets. These are passage, privacy, single dummy and double dummy. With passage and privacy sets there is also a backset choice of either 2 3/8" or 2 3/4".
Passage is the most commonly used and has knobs/levers that turn and operate a latch but there is no lock.
Privacy is like passage but there is a locking feature for bathrooms or bedrooms.
Single dummy is a surface mounted knob and plate for one side of a door with no functioning latch. Typically this is used for closet/pantry doors and ball or roller catches are used.
Double dummy is like single dummy but has trim for both sides of one door.
The diagrams below explain these functions in more detail.
The backset is the horizontal measurement from the edge of the door to the center of the hole bored through the door. On a lock or latch this is the distance from the front of the face plate to the center of the door knob hub. The backset of the lock or latch needs to match the backset of the pre drilled hole in order to install the hardware without modifying the door. Tubular latches for conversion doorsets are usually 2 3/8" or 2 3/4" backset.
See the diagram below for more detail.
Pre-drilled door prep for tubular latch installation