Parts of a Deadbolt Lock – Cylinder, Latch, Bolt, Strike

All 14 parts on the diagram

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Start here: 6 main parts 6

Cylinder The keyed unit on the outside of the door.
Thumbturn Throws and draws back the bolt from inside, with no key.
Bolt It has no spring: only the key or the thumbturn moves it.
Strike plate Fixed to the door frame; the bolt passes through it.
Deadbolt latch It carries the bolt and slides into the door's edge.
Faceplate The plate on the front of the latch, flush with the edge.

On the door 2

Cylinder housing The outside half of the lock; one maker calls it the escutcheon.
Rose A round trim plate; here it carries the thumbturn.

Taken apart 2

Torque blade (tailpiece) Runs through the latch to the thumbturn; either one moves the bolt.
Mounting screws They go in from inside and hold the two halves together.

In the frame 4

Dust box A small box set in the frame under the strike.
Strike reinforcer A metal plate behind the strike, held by long screws.
Backset From the door's edge to the center of the lock's hole.
Throw How far the bolt projects from the faceplate when it is locked.

How this list was compiled: Read 2026-09-30; a name is kept only where two of these use it. (1) Lock Industry Standards and Training Council, Locksmith Dictionary (2006), https://archive.org/details/locksmiths-dictionary : backset (the distance between the center of a cross-bore and the bolt edge of a door), bolt, cylinder, deadbolt (a bolt that needs a deliberate action to extend and resists end pressure when fully extended), dust box (an enclosure applied under a strike), face plate, rose (a usually circular escutcheon), single cylinder, double cylinder, strike, strike reinforcer (a metal plate mounted behind a strike, using long screws to secure it to the door frame), tailpiece (an actuator attached to the rear of the cylinder), throw (the distance a bolt or latch projects from the faceplate or case of a lock in the extended position), thumb turn. (2) A door hardware maker's installation instructions for its single cylinder deadbolt, https://archive.org/details/manualzilla-id-6930965 : deadbolt latch, latch housing, faceplate, cylinder, cylinder driver bar, thumbturn assembly, machine screws, dust box, door frame reinforcer, strike plate, backset. (3) A second maker's handleset and deadbolt installation guide, https://archive.org/details/manualzilla-id-6930943 : deadbolt latch, faceplate, outside cylinder housing, torque blade, thumbturn assembly, machine screws put through the thumbturn assembly into the outside cylinder housing, deadbolt strike plate, backset (the distance from the door edge to the center of the hole on the door face). (4) A third maker's deadbolt brochure, linked from https://www.pdqlocks.com/products/kt-deadbolt-lock : cylinder, bolt, throw, faceplate, strike, dust box, thumbturn, rose. (5) Bill Phillips, Locksmithing, https://archive.org/details/locksmithing-3rd-edition-bill-phillips : figure 2.48 (turnpiece rose assembly, mounting screws, reinforcing plate, deadbolt cylinder, full 1 inch throw deadbolt, torque blade), table 7.2, a fourth maker's deadbolt parts index (cylinder unit, cylinder bar, deadbolt with its throw and backset, rose and turn, mounting screws, cylinder housing), and its glossary (backset, deadbolt, strike plate, rose, tailpiece). (6) Wikipedia, Deadbolt: single cylinder and double cylinder, the bolt thrown into the door frame. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's lock, nothing traced. Licence: own work

How it works

These are the parts of a deadbolt, the lock set above the knob on an outside door: the cylinder outside, the thumbturn inside, and the latch in the door's edge that carries the bolt.

Read the full guide

On the door

The key goes in the cylinder, which sits in the cylinder housing on the outside. Inside, the thumbturn sits on a round plate called the rose. This is a single cylinder deadbolt: a key outside and a thumbturn inside.

In the door's edge and the frame

The deadbolt latch slides into a hole bored in the door's edge, and its faceplate sits on the edge. The torque blade runs from the cylinder through the latch to the thumbturn, so either one moves the bolt. The bolt passes through the strike plate into the dust box. Backset is the distance from the door's edge to the center of the lock; throw is how far the bolt sticks out.

Latches are made for a 2-3/8 inch or a 2-3/4 inch backset, so measure yours before ordering one.

Questions and answers

What are the parts of a deadbolt lock called?

Outside, the cylinder and its housing. Inside, the thumbturn on its rose. In the door's edge, the deadbolt latch with its faceplate and bolt, worked by the torque blade. On the frame, the strike plate, often with a reinforcer and a dust box.

What is the difference between a single and a double cylinder deadbolt?

A single cylinder deadbolt takes a key on one side and has a thumbturn on the other. A double cylinder deadbolt takes a key on both sides, so it has no thumbturn.

What is the backset of a deadbolt?

The distance from the edge of the door to the center of the hole bored through its face, where the cylinder sits. The latch has to match it.

What makes a deadbolt different from the latch in a doorknob?

A doorknob's latch bolt is held out by a spring and can be pushed back. A deadbolt has no spring: it moves only when the key or the thumbturn is turned.