Door lock types break down into deadbolts, knob and lever locks, mortise locks, and smart locks, each with distinct security and compatibility trade-offs.
Choosing the right door lock depends on where the door sits and how it is prepared. An exterior entry calls for a deadbolt; an interior bedroom door works fine with a privacy knob. The bore, backset, and door thickness decide what fits, and the ANSI/BHMA grade tells you how much abuse the lock can take.
Residential Mechanical Lock Types at a Glance
Deadbolts push a solid bolt into the strike plate and are not spring-loaded, with single-cylinder, double-cylinder, and vertical subtypes. Knob and lever locks put the cylinder in the handle assembly—common on interior doors but cautioned against as the sole exterior lock since the knob is easier to force. Mortise locks sit in a pocket cut into the door edge, with 2-, 3-, 4-, and 5-lever variants. Night latches (rim automatic deadlatches) are surface-mounted with a rim cylinder, while cylinder locks—including Euro and profile cylinders—house the pin/tumbler mechanism. Padlocks are portable, keyed or combination. Cam locks use a rotating arm for cabinets. Smart locks add electronics: multiple unlock methods beyond a key, dependent on battery power and, on many models, app connectivity.
What Door Dimensions Actually Matter
Three measurements decide fit: the bore hole diameter, backset, and door thickness. The standard US bore is 2-1/8 inches with a 1-inch cross bore. Backset—the distance from door edge to bore center—comes in 2-3/8 inches and 2-3/4 inches. Door thickness runs 1-3/8 inches for interior and 1-3/4 inches for exterior doors. Getting these wrong is the most common compatibility error: a 2-3/8 backset lock sits crooked on a 2-3/4 prep, and a 1-3/8-inch latch won’t throw correctly on a 1-3/4-inch slab. The US Army Corps of Engineers door hardware guide confirms this prep pattern; an example mortise specification shows a 1-3/4-inch standard thickness with a 2-3/4-inch backset.
Security Grades and Installation Prep
ANSI/BHMA grades measure lock durability. The ANSI/BHMA A156.2-2022 standard covers bored and preassembled locks, running cycle, strength, operational, material, finish, and dimensional tests—the full grading framework. Door prep decides installation: a bored lock fits round holes; a mortise lock needs a rectangular pocket cut into the door edge, so swapping between them is rarely direct. On exterior doors, pair a deadbolt with a secondary lock and verify the grade before purchase. Double-cylinder deadbolts add security but force a safety trade: egress requires the key immediately available inside, which matters for exits.
If you are ready to compare tested options for your front door, our roundup of the best door hardware locks breaks down the top picks side by side.
Which Lock Type Should You Actually Use?
For any exterior door, use a deadbolt, or a deadbolt plus a secondary lock. Interior doors can use knob or lever locks for privacy, and cabinet applications suit cam locks. Verify bore, backset, and door thickness against the standards above, then prefer hardware with a stated ANSI/BHMA grade.
| Lock Type | Best Use |
|---|---|
| Deadbolt | Exterior entry — primary lock |
| Knob or lever | Interior doors — not ideal as sole exterior lock |
| Mortise | Doors prepped with an edge pocket — often exterior-grade |
| Night latch | Secondary security on exterior doors |
| Cylinder lock | Residential doors with keyed cylinder mechanism |
| Padlock | Portable, freestanding security |
| Cam lock | Cabinets and drawers |
| Smart or keypad | Keyless convenience — depends on battery or app |
Match the lock type to the door’s job, measure the prep before buying, and let the ANSI/BHMA grade be your quality gauge.
FAQs
What is the difference between a deadbolt and a knob lock?
A deadbolt extends a solid bolt into the strike plate and is not spring-loaded, making it harder to force. A knob lock has the mechanism in the handle assembly, which is easier to defeat—discouraged as the only exterior lock.
Can I replace a mortise lock with a standard cylindrical lock?
Usually not as a direct swap. Bored locks need round prep holes; mortise locks sit in a rectangular edge pocket. Converting requires filling the mortise pocket and re-drilling, or installing an adapter plate—beyond a simple parts swap.
What does the ANSI/BHMA grade on a lock mean?
The grade certifies durability and strength. The ANSI/BHMA A156.2-2022 standard runs these cycle, strength, and material tests.
References & Sources
- ANSI Webstore. “Door Locking Standards.” Overview of ANSI/BHMA lock standards and grading.
- Builders Hardware Manufacturers Association. “ANSI/BHMA A156.2-2022 Locks and Latches.” Details on cycle and strength tests for Grade 1 and Grade 2.
- US Army Corps of Engineers. “Door Hardware Guide.” Standard bore, backset, and door thickness specifications.