Doorknobs, also called locksets, are classified as having bodies that are either cylindrical or mortise.
A cylindrical lockset has a rounded body that fits into a large hole bored into the door’s face and intersects with the latch bolt, which is inserted in a second, smaller hole drilled into the door’s edge.
Because this type of lockset does not include a security deadbolt, a second independent deadbolt lock must be added to the door if security is important.
A mortise lockset has a large, rectangular body that slides into a rectangular pocket (mortise) cut into the door’s edge.
The rectangular body of a mortise lockset contains the workings for the knob or lever handle, latch, and deadbolt.
With a mortise set, the knob is generally interconnected with a deadbolt–unlocking the deadbolt also frees the latch. Lock buttons at the door’s edge engage or disengage the lock.