KEY

in music, closed system of functionally related chords generated by certain tonal conventions associated with the Western concept of diatonic major and minor scales. Each of the pitches, or tones, used in Western music can serve as a tonic note, or keynote, for a major or minor key. Thus, the key of G major refers to a system of fixed relations between chords that is based on the tones of the major scale beginning on the note G, its tonic note. In musical notation, key is indicated by the key signature, a group of sharp or flat symbols at the beginning of each line of music. The concept of key is integral to the system of tonality (organization of notes, chords, and keys around a centrally important, or focal, tone). Different keys are closely or distantly related to one another according to the number of notes their diatonic scales share: the keys of C major and G major have six of their seven notes in common and are closely related. The distantly related keys of C major and C major have no notes in common. The ability of a listener to sense key relationships is exploited in musical forms such as the sonata. The broader term tonality is sometimes used as a synonym for key. in locksmithing, an instrument, usually of metal, by which the bolt of a lock (q.v.) is turned. The Romans invented metal locks and keys and the system of security provided by wards. This system was, for hundreds of years, the only method of ensuring that only the right key would rotate in the keyhole. The wards are projections around the keyhole (inside the lock) that make it impossible for a plain key to be turned in it. If, however, the key has slots cut in it that correspond to the projections, the slots clear the projections, the key can be turned, and the bolt is thrown back. Throughout the centuries immense ingenuity was exercised by locksmiths in the design of the wards, and, consequently, some keys are very complicated. All the same, it was not difficult to make an instrument that could be turned in spite of the wards, to achieve what is known as picking a lock. Little progress was made in the mechanism of the lock and key until the 18th century, when a series of improvements began that led, in the 1860s, to the development of the Yale cylinder lock, with its thin, convenient key capable of many thousands of variations. The key is made in a number of different cross sections so that only a particular variety of key will fit into a particular keyhole; this, in effect, is a form of ward. The serrations on the edge of the key raise pin tumblers to exactly the correct height, allowing the cylinder of the lock to revolve and withdraw the bolt. Although not impossible to pick, these locks are convenient and compact and offer a reasonable degree of security. In the late 20th century they were the most usual form of fastening for an outside door and were made by locksmiths in all parts of the world. A special system is that of the master key. This system is used when a number of locks (such as those securing bedrooms in a hotel), each having a different key, must all be opened by a landlord or caretaker using a single key. Where the only security is by wards, a skeleton key that avoids the wards may be the type of master key chosen. In other cases, many methods are employed; for instance, there may be two keyholes (one for the servant key, the other for the master), or two sets of tumblers or levers, or two concentric cylinders in a Yale lock. in machine construction, a device used to prevent rotation of a machine component, such as a gear or a pulley, relative to the shaft on which it is mounted. A common type of key is a square bar that fits half in a groove (keyway) in the shaft and half in an adjoining keyway in the component. If the shaft and the key are of the same material, a key with a width and depth equal to one fourth of the shaft diameter will have the same torque capacity as the solid shaft if its length is 1.57 times the shaft diameter. These proportions are closely approximated in practice.