Deadbolts: Bolts That Must Be Deliberately Thrown

Terms

LIST defines the common deadbolt vocabulary:

• Deadlock. "A lock which incorporates a deadbolt."
• Auxiliary lock. "Any lock installed in addition to the primary lockset." Most residential deadbolts are auxiliary locks.
• Single cylinder. "Pertaining to a lock with key operation from only one side." The other side usually has a thumbturn.
• Double cylinder deadlock. "A deadbolt lock whose bolt may be operated by a key from either side."
• Throw. "The distance a bolt or latch projects from the faceplate or case of a lock in the extended position."
• Deadlocking latch. "A latchbolt with a deadlocking mechanism." This is a self-latching bolt that resists end pressure once the door is closed. It is not the same thing as a deadbolt.
• Interconnected lockset. A lockset "whose trim provides a means of simultaneous retraction of two or more bolts which may also be operated independently." One turn of the inside lever pulls back both the latch and the deadbolt.

How a Deadbolt Works

A cylinder or thumbturn rotates a cam or tailpiece. LIST defines a cam as the component that "transfers the rotational motion of a key or cylinder plug to the bolt works of a lock." That motion slides the bolt out into the strike in the door frame, or pulls it back. Nothing spring-loaded pushes it out, which is why closing the door does not lock it. When fully thrown, the bolt mechanism resists being pushed back from the end. That is the "resists end pressure" part of the LIST definition.

How well the bolt holds depends on more than the lock:

• The bolt. Manufacturers publish throw and bolt construction. Schlage's spec sheets, for example, list a 1" (25 mm) throw for its B500 and B600 series, with a hardened steel roller inside the bolt.
• The strike and frame. The bolt is only as strong as what it engages. Schlage's B500 sheet describes a concealed frame reinforcer under the strike, anchored to the jamb "with three 3" (76 mm) long screws," which it says strengthens a wood jamb against "kick-in" attack. These figures are one manufacturer's specification, not a code or standard. See strike plates.
• The cylinder. The key side of a deadbolt is a lock cylinder like any other. Higher-security cylinders are covered under high-security locks and UL 437.

Standards and Grades

Two current ANSI/BHMA standards cover North American deadbolts, and they grade differently.

ANSI/BHMA A156.36, Auxiliary Locks. BHMA's summary of the 2020 edition says the standard covers dimensional criteria and "five classifications of tests: operational, cycle, strength, security and, finish." Examples it gives:

• Cycle. "Grade 1 dead locks… must pass a rigorous test through 250,000 cycles of opening and closing."
• Security. "Seven aggressive tests are specified, including a 1350 pound force on the door against the dead bolt for Grade 1."
• Operation. "Key operated locks must open with a maximum torque of 9 lbf-in."

A156.36 also numbers lock functions. BHMA lists "dead bolt operated by key from either side" (double cylinder) and "dead bolt operated by key from outside and by turn from inside" (single cylinder) among its examples. See lock functions.

ANSI/BHMA A156.40, Residential Deadbolts. The current edition is 2025. BHMA's summary covers residential deadbolts and deadlatches, with durability, security, and finish tests. It uses letter grades. "Grade A residential dead latches, for example, must pass a rigorous test that requires 400,000 cycles." It specifies "seventeen aggressive tests… including one that includes loading the door against the deadbolt with 1,350 pounds of force." Corrosion resistance is checked with an ASTM B117 salt spray test.

Cycle figures belong to specific standards and product types. The 800,000 and 1,000,000 cycle figures often quoted for "Grade 1" come from the bored-lockset standard, A156.2, not from deadbolt standards. See ANSI/BHMA lock grades. Some manufacturer sheets still cite the older designation "ANSI A156.5" for their deadbolts. Schlage's B500 sheet lists "ANSI A156.5, 2001, Grade 2," for example. When comparing products, check which standard and edition a grade refers to.

Codes: Egress and Fire Doors

Deadbolts on doors that people use to get out of a building are regulated by codes, and the rules depend on where the door is. The summary below follows Lori Greene's explanations of the model codes on I Dig Hardware. Local adoptions and amendments vary, so the adopted code for a project governs.

• One releasing motion. "Doors in a means of egress must unlatch with one releasing motion – with a few exceptions." Greene notes that IBC "bolt locks" are a separate code category and do not address deadbolts.
• Dwelling and sleeping units. The IBC allows a deadbolt or other security device in addition to the latch on Group R dwelling and sleeping units. These must be "operable from the inside without the use of a key or tool" and need only one additional releasing operation. The IBC limits this to units with an occupant load of 10 or less.
• Homes under the IRC. Section R311.2 requires that egress doors "be readily openable from inside the dwelling without the use of a key or special knowledge or effort." Greene notes that a thumbturn deadbolt is typically acceptable on these doors, but "a double-cylinder deadbolt does not meet the IRC's requirements for a lock on an egress door."
• Key-operated locks on commercial main doors. The IBC allows key-operated locks in certain occupancies: assembly occupancies with an occupant load of 300 or less, business, factory, mercantile, storage, and places of religious worship. The lock must be "readily distinguishable as locked," and the door needs a sign reading "THIS DOOR TO REMAIN UNLOCKED WHEN THIS SPACE IS OCCUPIED."
• Fire doors. "Deadbolts on fire doors must be labeled." Fire door hardware is tested to UL 10C / NFPA 252, and NFPA 80 requires components of a fire door assembly to be listed or labeled. BHMA notes that hardware for fire doors under A156.36 "is evaluated and listed to UL 10C." See fire-rated door hardware.

Variations

• Mortise deadbolts. The bolt sits in a lock case set into a pocket in the door edge, sometimes alongside a latch. See mortise locks.
• Rim deadlocks. These mount on the inside face of the door. LIST defines a rim lock as "a lock or latch typically mounted on the surface of a door." See rim and mortise cylinders.
• Multipoint locks. Several bolts are thrown at once along the door edge. See multipoint locks.
• Electronic and smart deadbolts. See electronic locks and smart locks.
• Changing keys. A deadbolt's cylinder can often be rekeyed without replacing the lock. See rekeying locks.

Related Topics

• Strike plates
• ANSI/BHMA lock grades
• UL 437
• Cylindrical locks
• Mortise locks
• Lock functions
• Fire-rated door hardware
• Multipoint locks
• Smart locks
• Kwikset
• Rekeying locks

Sources