A mortise lock (mortice lock in British English) is a lock that requires a pocket—the mortise—to be cut into the door or piece of furniture into which the lock is to be fitted. In most parts of the world, mortise locks are found on older buildings constructed before the advent of bored cylindrical locks, but they have recently become more common in commercial and upmarket residential construction in the United States. They are widely used in domestic properties of all ages in Europe.
Mortise locks may include a non-locking sprung latch operated by a door handle. Such a lock is termed a sash lock. A simpler form without a handle or latch is termed a ‘dead lock’. Dead locks are commonly used as a secure backup to a sprung non-deadlocking latch, usually a pin tumbler rim lock.[note 1]
Mortice locks have historically, and still commonly do, use lever locks as a mechanism. Older locks may have used warded locks. This has led to a popular confusion between the two; the term ‘mortice lock’ is widely known and used, but usually in reference to lever keys. In recent years the Euro cylinder lock has become common, using a pin tumbler lock in a mortice housing.
The parts included in the typical US mortise lock installation are the lock body (the part installed inside the mortise cut-out in the door); the lock trim (which may be selected from any number of designs of doorknobs, levers, handle sets and pulls); a strike plate, or a box keep, which lines the hole in the frame into which the bolt fits; and the keyed cylinder which operates the locking/unlocking function of the lock body. However, in the United Kingdom, and most other countries, mortise locks on dwellings do not use cylinders, but have lever mechanisms.
The installation of a mortise lock can be undertaken by the average homeowner with a working knowledge of basic woodworking tools and methods. Many installation specialists use a mortising jig which makes precise cutting of the pocket a simple operation, but the subsequent installation of the external trim can still prove problematic if the installer is inexperienced.
Although the installation of a mortise lock actually weakens the structure of the typical timber door, it is stronger and more versatile than a bored cylindrical lock, both in external trim, and functionality. Whereas the latter mechanism lacks the architecture required for ornate and solid-cast knobs and levers, the mortise lock can accommodate a heavier return spring and a more solid internal mechanism, making its use possible. Furthermore, a mortise lock typically accepts a wide range of other manufacturers’ cylinders and accessories, allowing architectural conformity with lock hardware already on site.
Some of the most common manufacturers of mortise locks in the United States are Accurate, Arrow, Baldwin, Best, Corbin Russwin, Emtek, Falcon, Penn, Schlage, Sargent and Yale Town & Lock. Also, many European manufacturers whose products had been restricted to “designer” installations have recently gained wider acceptance and use.
Mortice Lock Standards
There are several different standards for mortice locks in use. The most common are:
British Standard (small)
- Faceplate length: 152.5mm (6 inches)
- Backset:44.5mm (1¾ inches)
- C/C(lever lock): 57mm (2¼ inches).
- C/C(bathroom mortise lock): 57mm(2¼ inches).
- Used in internal doors.
British standard (large), BS3621
- Faceplate length: 176mm (7 inches).
- Backset: 57mm (2¼ inches).
- C/C(lever lock): 57mm (2¼ inches).
- C/C(cylinder lock): 45mm (≈ 1¾ inches).
- Used in entrance doors.
- Note: Many insurance policies require homes to install a BS3621 lock because its 5 lever deadbolt is believed to provide increased security.
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