the medieval period and up until early 19th century. Three English locksmiths, Robert Barron, Joseph Bramah, and Jeremiah Chubb, all played a role in creating modern lever tumbler locks. Chubb's lock was patented in 1818. Again, the term refers to the lock mechanism, so a lock can be both a mortise lock and a lever tumbler lock. In the modern lever tumbler lock, the key moves a series of levers that allow the bolt to move in the door. The next major innovation to mortise lock mechanisms came in 1865. Linus Yale, Jr.'s pin tumbler mortise cylinder lock put not only the latch or bolt itself inside the door, but also the tumblers and the bolt mechanism. Up to this point, the lock mechanism was always on the outside of the door regardless of the bolt location. This innovation allowed keys to be shorter as they no longer had to reach all the way through a door. Pin tumbler locks are still the most common kind of mortise lock used today. Mechanism 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. Mortise locks have historically, and still commonly do, use lever locks as a mechanism. Older mortise locks may have used warded lock mechanisms. This has led to popular confusion, as the term "mortise lock" was usually used in reference to lever keys in traditional European terminology. In recent years the Euro cylinder lock has become common, using a pin tumbler lock in a mortise 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 box keep), which lines and reinforces the cavity in the door jamb or frame into which the bolt fits; and the keyed cylinder which operates the locking/unlocking function of the lock body. Selection and installation The installation of a mortise lock can be undertaken by an average homeowner with a working knowledge of basic woodworking tools and methods. Many installation specialists such