A standard doorknob lock set consists of a pair of knobs, one on each side of the door, that are connected through the door by a spindle and held together by mounting bolts. The spindle runs through the latch bolt, which is inside the door perpendicular to the spindle. The latch bolt is connected to the latch, which protrudes from the edge of the door and engages the door frame, preventing the door from opening.
Knobs, Spindle and Latch
When either knob turns, it rotates the spindle, and the spindle retracts the latch and allows the door to open. In most cases, the spindle is spring-loaded so that the latch springs back into the closed position when the doorknob is released.
Face Plate and Strike Plate
The face plate is a flat metal plate on the edge of the door through which the latch protrudes; it is secured to the door with screws and holds the latch in place. The metal strike plate is attached to the door frame opposite the latch; its job is to guide the latch into its receptacle in the frame and hold it securely closed.
Knob Sets and Locks
Interior passage doorknob sets are not equipped with locks, and in this case, both knobs always turn freely, and either knob can retract the latch. Privacy knob sets for interior doors are equipped with a keyless lock on the inside knob; in these knob sets, turning or pushing a button on the inside knob prevents the outside knob from turning and opening the door, but turning the inside knob releases the lock and allows the door to open.
Entry knob sets are typically equipped with a keyed lock on the outside knob and a button-activated lock on the inside knob. The button lock on the inside knob works the same way that it does on a privacy knob set, but the door can also be opened from the outside with the use of a key.
Lever Sets and Handle Sets
As an alternative to knob sets, some lock sets are equipped with levers or grip handles rather than doorknobs. In the case of a lever set, a lever handle rotates the spindle and retracts the latch when the lever is pushed downward. In a handle set, the latch retracts when a thumb piece on the handle is depressed, engaging an internal lever, which in turn rotates the spindle and opens the latch.