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lock and key

lock and key, fastening fitted to an entryway, such as a gate or door, or a container, such as a cabinet, drawer or safe, to keep it closed and/or prevent unauthorized access or use. Locks typically consist of a sliding, pivoted, or rotary bolt protected by a fixed or movable object. A lock may be opened by a mechanical, magnetic, electric, electronic, or electromechanical key or by employing a code or sequence of numbers or letters.

Mechanical Locks

There are two basic types of mechanical locks, each with variations. The oldest and simplest is the warded lock, which is essentially a spring-loaded bolt in which a notch has been cut. The key fits into the notch and slides the bolt backward and forward. The lock takes its name from the fixed projections, or wards, inside the lock and around the keyhole. The correct key has notches cut into it that match the wards, which block the wrong key from operating the lock. The ward lock is the easiest to pick and now is used only for cheap padlocks.

The tumbler lock contains one or more pieces of metal (called tumblers, levers, or latches) that fall into a slot in the bolt and prevent it being moved. The proper key has serrations that raise the metal pieces to the correct height above the slot, allowing the bolt to slide. There are three types of tumbler locks, pin-tumbler, disk-tumbler, and lever-tumbler. Pin-tumbler locks are the most common. The tumblers in this type of lock are small pins. The modern door lock is a compact pin-tumbler cylinder lock of the type developed (1860) by the American inventor Linus Yale. Door locks on automobiles and most high-security locks have pin tumblers. Disk- or wafer-tumbler locks, use flat disks, or wafers, instead of pins. When the proper key is inserted, the disks retract, releasing the bolt. Disk-tumbler locks are often used in desks and file cabinets. Lever-tumbler locks employ a series of different-sized levers resting on a bolt pin to prevent the bolt from moving. When the proper key is inserted, all the levers are raised to the same height, enabling the bolt pin to release the bolt. Lever-tumbler locks are often used in briefcases, safe-deposit boxes, and lockers.

The first of the keyless locks was the combination lock, developed at the beginning of the 17th cent. In it a number of rings inscribed with letters or numbers are threaded on a spindle. To open the lock the rings must be turned to form a code word or number, which causes the slots inside the rings to align and permits the spindle to be drawn out. A variant of the combination lock employs a movable dial with a series of numbers around it in place of the rings. The dial must be turned clockwise and counterclockwise in the proper sequence of numbers to align disk tumblers and open the lock. Once used only for padlocks, combination locks began to be used in safes and strong-room doors during the last half of the 19th cent. The time lock, first used successfully c.1875, has a clock mechanism that is set to permit opening only a certain time.

Electric and Magnetic Locks

Recent lock developments include the magnetic-key lock, in which the pins are actuated by small magnets on the key, which has no serrations. When the key is inserted into the lock, these magnets repel magnetized spring-loaded pins, raising them in the same way that the serrations on a tumbler-type key would. The card-key lock is actuated by a series of magnetic charges; the card-key is popular where security is vital, because a new series may be electronically defined for each new user, without having to change the lock itself. Similarly, electronic card access systems are used in many hotels and office buildings. A special "key" system uses a paperboard or plastic card, on which a code is recorded as a series of holes or bumps, or a microchip or a magnetic strip on which a code is stored. A card reader at the lock location reads the code and sends the information to a computer, which sends a signal to release the bolt if the code is correct. Electronic combination locks similarly use a computer to compare a combination stored in memory with one entered on a keypad; access is permitted if the combinations match. In a biometric entry system the numeric keypad is replaced by a scanner, which captures an individual's fingerprint, palmprint, signature, or other personal characteristic and compares it with that in the computer's memory. Biometric entry systems are most often used in high-security areas, such as nuclear power plants.

In an electromagnetic lock a metal plate is attached to the door and an electromagnet is attached to the doorframe opposite the plate. When the current flows, the electromagnet attracts the plate, holding the door closed, When the flow of current is stopped, the door unlocks. A variation places the plate and electromagnet so that the door is held open when current flows, enabling the door to be closed automatically when the current stops.

Keyless entry systems, which are common in motor vehicles, rely on a keychain fob that contains a remote-control unit consisting of an integrated circuit and a radio transmitter. The fob sends a low-powered radio signal to a receiver in the motor vehicle, and, if the received code is the correct one, the receiver in the vehicle relays the signal to a microprocessor, which opens the lock. The acceptance of such entry systems has led to devices that allow additional functions within the vehicle to be activated remotely.

In other keyless entry systems, radio-frequency identification (RFID) is used. An RFID tag, card, or fob is brought within range of radio waves produced by an RFID reader or interrogator, allowing data to be exchanged; when the microprocessor controlling the lock confirms that the received data is associated with someone allowed entry, the door is unlocked. RFID systems are more commonly used to control entry into buildings or rooms, and the use of a computer to control locks that use RFID allows access to specific areas to be restricted to specific people or at specific times.

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Locks and Keys

Locks and Keys

Locks can be either mechanical or electronic, the latter being a modern variation for which a specific numeric code is required to release the locking mechanism. Much more common is a mechanical lock, opened by purely physical means. Locks do not have an independent existence; they must lock something or someone in or out, and they must have a key. The key is based on principles that go back to ancient times, using one of the most rudimentary types of machine known to humankind: the inclined plane.

Historical background. In the history of physics and technology, there are three simple machines: the lever, the inclined plane, and the hydraulic press. The last of these only came into existence during the 1600s, but the first two date to a time before the dawn of civilization. The simplest form of inclined plane is a ramp, which makes it possible to move an object across a vertical distance with a smaller amount of exertion than would be required to lift it straight upward. Other modifications of the inclined plane are wedges, knives, axes, screws, corkscrews, and a key and lock mechanism.

The earliest locks date back to ancient Egypt, and even the more modern variations on lock design that developed in the wake of industrialization still harken back to the design used in the pharaohs' palaces. For example, American locksmith and inventor Linus Yale, Jr., whose name remains an important one in the lock and key industry, based his cylinder lock in the 1860s on the Egyptian design. The latter consisted of a wooden housing containing wooden pegs of varying length, fitted into holes bored into the top of a wooden bolt. Only when a long wooden key with pegs of specific lengths was inserted into the bolt could it be opened.

Basic workings of a lock. Modern locks and keys are made of steel rather than wood, but otherwise the design is not remarkably different from that used to lock doors thousands of years ago. Inside a modern mechanical lock is a row of pins, usually five in number. Each pin has its own cylinder, and when the lock is locked, they hold together two pieces of metal rather as the "teeth" of a belt hold together two sections of a piece of leather. The pins are of varying length, meaning that in order to open the lock, it is necessary to raise them all together so that the bottoms are in alignment.

The solution to this problem is, quite literally, a key, whose serrated edge is actually a row of inclined planes fitted to the configuration of pins inside the lock. The notches on the key are made to push the pins upward just the right amount for each pin, so as to force them all into their respective cylinders and separate the two blocks from one another. The shape of the notches is such that the key can be withdrawn from the lock after use, at which point springs push the pins back downward into their original place.

Mechanical and electronic variations. A variation on this model is Yale's cylinder lock. In this design, the pins are lined up along a larger metal cylinder, which they hold in place inside a cylindrical housing. Inserting the proper key raises the pins and frees the cylinder so that, when it is turned, it rotates and draws back a cam that holds a bolt in place. The bolt is spring-loaded, such that when the key is withdrawn, the spring pushes the bolt back into place, turning the cylinder back to its original position and making it possible to withdraw the key.

There are other variations on the mechanical lock, most notably the old-fashioned lever lock, but the basic principle is the same. By contrast, an electronic lock requires the use of a keypad and a numeric code. The user enters a code, which the machine interprets as a series of binary (on-off) electric pulses. These pulses are bits in a number sequence, which are read by a computer chip. Assuming the sequence matches the one encoded on the chip, the latter sends out an electric signal that opens a mechanical bolt holding the lock in place.

FURTHER READING:

BOOKS:

Macaulay, David, with Neil Ardley. The New Way Things Work. Boston: Houghton Mifflin, 1998.

Phillips, Bill. The Complete Book of Locks and Locksmithing. New York: McGraw-Hill, 1995.

Roper, C. A. The Complete Book of Locks and Locksmithing. Blue Ridge Summit, PA: Tab Books, 1983.

Sloane, Eugene A. The Complete Book of Locks, Keys, Burglar and Smoke Alarms, and Other Security Devices. New York: Morrow, 1977.

SEE ALSO

Black Ops
Covert Operations
Lock-Picking

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lock-and-key theory

lock-and-key theory A theory to explain the mechanism of enzymatic reactions, in which it is proposed that the enzyme and substrate(s) bind temporarily to form an enzyme–substrate complex. The binding site on the enzyme is known as the ‘active site’ and is structurally complementary to the substrate(s). Thus, the enzyme and substrate(s) are said to fit together as do a lock and a key.

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lock-and-key theory

lock-and-key theory A theory to explain the mechanism of enzymatic reactions, in which it is proposed that the enzyme and substrate(s) bind temporarily to form an enzyme–substrate complex. The binding site on the enzyme is known as the ‘active site’ and is structurally complementary to the substrate(s). Thus the enzyme and substrate(s) are said to fit together as do a lock and a key.

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locks and keys

locks and keys A system of memory protection in which segments of memory are assigned identification numbers (the locks) and authorized users are provided the numbers (the keys) by the operating system. This provision is done by a privileged process in some location, such as a program status word, not accessible to the user.

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Lock and Key

Lock and Key

Resources

A lock and key refers to the combination that enables a door to be securely closed. The combination relies upon the individual fit of a protruding object (the key) and a receptor (the lock). In biology, an analogous scheme determines the specific reaction of an antigen with an antibody, and between a protein receptor and the target molecule.

The lock originated in the Near East, and the earliest known lock to be operated by a key was the Egyptian lock. Possibly 4,000 years old, this large wooden lock was found in the ruins of the palace of Khorsabad near Nineveh, the ancient capital of Assyria. The Egyptian lock is also known as the pin-tumbler type, and it evolved as a practical solution to the problem of how to open a barred door from the outside. The first and simplest locks were probably just a bar of wood or a bolt across a door. To open it from the outside, a hand-size opening was made in the door. This evolved into a much smaller hole into which a long wooden or metal prodder was inserted to lift up the bar or bolt. The Egyptians improved this device by putting wooden pegs in the lock that fell into holes in a bolt, which meant that the bolt could not be moved until the pegs were lifted out. This was done by giving the long wooden key some corresponding pins that lifted out the pegs from the holes in the bolt so it could be drawn back. These locks were up to 2 ft (61 cm) long and their keys were long, wooden bars resembling a toothpick. It was this invention of tumblerssmall, movable wooden pegs that fell by their own weight into the boltthat would eventually form the basis of modern types of locks.

The ancient Romans built the first metal locks, and their iron locks and bronze keys are easily recognizable even today. They improved the Egyptian model by adding wardsprojections or obstructions inside the lockthat the key must bypass in order to work. Besides these warded locks, the Romans also invented the portable padlock with a U-shaped bolt which is known to have been invented independently by the Chinese. Some Roman locks used springs to hold the tumblers in place, and the Romans made locks small enough that they could wear tiny keys on their fingers like rings. In medieval times, locks and keys changed little in design, with most of the effort directed at making them more elaborate and beautiful. It was during this time that lock making became a skilled trade, and although there were some design changes, like a pivoted tumbler and more complicated wards, medieval locks are characterized mainly by their high degree of lavish embellishment. Despite this high level of medieval craftsmanship, these medieval locks did not provide a great deal of security against the determined and skilled thief, and even with especially elaborate warding systems, they were still relatively easy to pick or open.

The modern age of the lock and key is usually said to have begun in 1778 in England when Robert Barron first patented his double-acting tumbler lock. Also called the multiple tumbler, this ingenious design was a major advance in lock security and established the principle of all lever locks. Barrons new lock had two tumblers, which are really levers, that had to be raised to exactly the right height for the lock to open. Unless a properly notched key was used to raise each tumbler, the lock would not open. His lock could still be picked by a determined individual however, and in 1818 Jeremiah Chubb was able to improve Barrons lock by adding a convict-defying detector. This was a spring or a special lever that was activated if any tumbler was raised too high. The lock would then jam, both preventing the bolt from releasing and showing the owner that the lock had been tampered with. Real lock security was not achieved however until English engineer Joseph Bramah (1748-1814) first introduced his pick-proof lock in 1784, after Barrons lock but before Chubb. Bramahs lock was exhibited in his shop window with a sign offering a substantial sum to anyone who could pick it. The offer outlived Bramah whose lock remained unopened for over 50 years until a skilled American mechanic finally picked it open after 51 hours of effort.

Bramahs 4 in (10 cm), hand-made, iron padlock was impervious because of its extreme complexity, and he soon found that he could not produce enough locks to meet the growing demand by using traditional methods. His locks used a notched diaphragm plate and a number of spring-loaded radial slides that were pushed down by a notched key until they matched the notches on the diaphragm. Producing such precision instruments on a large scale necessitated precision machine tools, and with the help of English engineer Henry Maudslay (1771-1831), Bramah produced a series of machines that were among the first machine tools designed for mass production. Thus the simple lock and key were at the forefront of a revolution in manufacturing, heralding the standardization and interchangeability of parts and division of labor that would characterize modern methods of mass production.

By the mid-nineteenth century, the lock industry was in full force and was attempting to meet the growing demands of an economy spurred by the Industrial Revolution. In 1861, the American inventor Linus Yale Jr. (1821-1868) produced the Yale cylinder lock that was based on the pin-tumbler mechanism of the ancient Egyptians. This type of lock is still the most common type used today, and it uses a small, flat key whose serrated edges raise five pins in the cylinder to proper heights and make it possible to turn the cylinder. Varying the lengths of these five pins combined with other slight internal changes, allowed for millions of possible combinations, meaning that practically no two notched keys are alike. In an odd twist on conventional wisdom, it could be said that Yale took advantage of mass production methods to manufacture unidentical articles, since he made each set of lock and key slightly different from the one before it. While still not infallible, Yale cylinder locks are quite difficult to pick and offer reasonable security under ordinary circumstances. This style of lock and key is the most familiar and the most generally used to secure the outside doors of buildings and automobiles.

Keyless combination locks have been known since the sixteenth century. They contain a series of rings or tumblers threaded on a spindle that must be turned from the outside in such a way that all the rings line up. These rings usually have numbers or letters on them, and if a lock has three rings with 100 numbers on each, there are approximately one million possible combinations, only one of which will open the lock. Combination locks have no keyholes in which to pry or insert explosives, and they became popular for safes and vaults. They are often used in conjunction with time-lock devices, preventing a safe or door from being opened during certain hours even if the correct combination is used.

Altogether, todays mechanical locks are variations of the three basic types of locks: the early Bramah lever, the Yale cylinder, and the combination lock. Sometimes a single lock may combine some features of each, such as a Finnish combination lock whose rings must be moved to the proper position by a the turn of a key. In the United States in the 1970s, electronic locks that worked on the same principle as the touch-tone phone became popular. When the correct sequence of spring-loaded buttons was pushed, the door would open. This system used no keys, proved to be as tamper-proof as any traditional combination lock, and allowed the touch-tone sequence to be changed at any time. Magnetism has also been used to operate a Yale-type lock. These locks had keys with no serrations but rather contained several small magnets. Insertion of the key allowed its magnets to repel magnetized spring-loaded pins inside the lock, which were raised to open it. The newest lock and key systems do not use anything recognizable as a traditional lock or key. Increasingly, todays hotels are switching to special plastic cards with magnetic strips on them. Like a key, they are inserted, but only momentarily, into a slot usually just above the doorknob. Often a small green light flickers after withdrawal, and the door opens if the doorknob is turned. These cards open the door using electronic systems.

KEY TERMS

Combination lock One which is operated by a rotating dial by which certain numbers or letters in a particular order, after a given number of turns in the prescribed direction, are brought opposite the setting mark, after which the lock can be opened.

Cylinder The part of a cylinder lock that provides the security. It consists of a short cylindrical plug containing the key hole and mechanism, adjustable by the key.

Spindle The shaft of a knob or handle, usually square, which passes through the follower to enable the handle, when turned, to operate the spring bolt.

Tumbler A part to retain the bolt or provide security in certain locks. In England, this part is called a lever.

Ward A fixed projection in a lock to prevent a key from entering or turning, unless it is properly shaped.

Locks and keys may change considerably over time, but the universal human need to keep other people away from ones possessions will remain as important to future generations as it did to the ancient Egyptians.

Resources

BOOKS

Fu, Haian. Protein-Protein Interactions: Methods and Applications. Totowa, NJ: Humana Press, 2004.

McCloud, Mark and Gonzales De Santos. Lock Picking Basics. Champaign, IL: Standard Publications, 2004.

Phillips, Bill. The Complete Book of Locks and Locksmithing. New York: McGraw-Hill Professional, 2005.

Leonard C. Bruno

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Lock and Key

Lock and key

A lock is a mechanical device for securing a door, chest, or other receptacle so that it can only be opened by an authorized person. Most locks are opened by a key which is placed in the lock and turned. Combination locks do not use a key but rather have a cylinder that is turned to certain stops. Today, many hotels use special plastic cards with magnetic strips as keys which cause a door to open electronically when inserted in a slot near the doorknob.


History

The lock originated in the Near East, and the earliest known lock to be operated by a key was the Egyptian lock. Possibly 4,000 years old, this large wooden lock was found in the ruins of the palace of Khorsabad near Nineveh, the ancient capital of Assyria. The Egyptian lock is also known as the pin-tumbler type, and it evolved as a practical solution to the problem of how to open a barred door from the outside. The first and simplest locks were probably just a bar of wood or a bolt across a door. To open it from the outside, a hand-size opening was made in the door. This evolved into a much smaller hole into which a long wooden or metal prodder was inserted to lift up the bar or bolt. The Egyptians improved this device by putting wooden pegs in the lock that fell into holes in a bolt, which meant that the bolt could not be moved until the pegs were lifted out. This was done by giving the long wooden key some corresponding pins that lifted out the pegs from the holes in the bolt so it could be drawn back. These locks were up to 2 ft (61 cm) long and their keys were long, wooden bars resembling a toothpick. It was this invention of tum blers—small, movable wooden pegs that fell by their own weight into the bolt—that would eventually form the basis of modern types of locks.

The ancient Romans built the first metal locks, and their iron locks and bronze keys are easily recognizable even today. They improved the Egyptian model by adding wards—projections or obstructions inside the lock—that the key must bypass in order to work. Besides these warded locks, the Romans also invented the portable padlock with a U-shaped bolt which is known to have been invented independently by the Chinese. Some Roman locks used springs to hold the tumblers in place, and the Romans made locks small enough that they could wear tiny keys on their fingers like rings. In medieval times, locks and keys changed little in design, with most of the effort directed at making them more elaborate and beautiful. It was during this time that lock-making became a skilled trade, and although there were some design changes, like a pivoted tumbler and more complicated wards, medieval locks are characterized mainly by their high degree of lavish embellishment. Despite this high level of medieval craftsmanship, these medieval locks did not provide a great deal of security against the determined and skilled thief, and even with especially elaborate warding systems, they were still relatively easy to pick or open.


Modern locks

The modern age of the lock and key is usually said to have begun in 1778 in England when Robert Barron first patented his double-acting tumbler lock. Also called the multiple tumbler, this ingenious design was a major advance in lock security and established the principle of all lever locks. Barron's new lock had two tumblers, which are really levers, that had to be raised to exactly the right height for the lock to open. Unless a properly notched key was used to raise each tumbler, the lock would not open. His lock could still be picked by a determined individual however, and in 1818 Jeremiah Chubb was able to improve Barron's lock by adding a "convictdefying detector." This was a spring or a special lever that was activated if any tumbler was raised too high. The lock would then jam, both preventing the bolt from releasing and showing the owner that the lock had been tampered with. Real lock security was not achieved however until English engineer Joseph Bramah (1748-1814) first introduced his pick-proof lock in 1784, after Barron's lock but before Chubb. Bramah's lock was exhibited in his shop window with a sign offering a substantial sum to anyone who could pick it. The offer outlived Bramah whose lock remained unopened for over 50 years until a skilled American mechanic finally picked it open after 51 hours of effort. Bramah's 4 in (10 cm), hand made, iron padlock was impervious because of its extreme complexity, and he soon found that he could not produce enough locks to meet the growing demand by using traditional methods. His locks used a notched diaphragm plate and a number of spring-loaded radial slides that were pushed down by a notched key until they matched the notches on the diaphragm. Producing such precision instruments on a large scale necessitated precision machine tools , and with the help of English engineer Henry Maudslay (1771-1831), Bramah produced a series of machines that were among the first machine tools designed for mass production . Thus the simple lock and key were at the forefront of a revolution in manufacturing, heralding the standardization and inter-changeability of parts and division of labor that would characterize modern methods of mass production.

By the mid-nineteenth century, the lock industry was in full force and was attempting to meet the growing demands of an economy spurred by the Industrial Revolution . In 1861, the American inventor Linus Yale Jr. (1821-1868) produced the Yale cylinder lock which was based on the pin-tumbler mechanism of the ancient Egyptians. This type of lock is still the most common type used today, and it uses a small, flat key whose serrated edges raise five pins in the cylinder to proper heights and make it possible to turn the cylinder. Varying the lengths of these five pins combined with other slight internal changes, allowed for millions of possible combinations, meaning that practically no two notched keys are alike. In an odd twist on conventional wisdom, it could be said that Yale took advantage of mass production methods to manufacture unidentical articles, since he made each set of lock and key slightly different from the one before it. While still not infallible, Yale cylinder locks are quite difficult to pick and offer reasonable security under ordinary circumstances. This style of lock and key is the most familiar and the most generally used to secure the outside doors of buildings and automobiles.

Keyless combination locks have been known since the sixteenth century. They contain a series of rings or tumblers threaded on a spindle which must be turned from the outside in such a way that all the rings line up. These rings usually have numbers or letters on them, and if a lock has three rings with 100 numbers on each, there are approximately one million possible combinations, only one of which will open the lock. Combination locks have no keyholes in which to pry or insert explosives , and they became popular for safes and vaults. They are often used in conjunction with time-lock devices, preventing a safe or door from being opened during certain hours even if the correct combination is used.

Altogether, today's mechanical locks are variations of the three basic types of locks: the early Bramah lever, the Yale cylinder, and the combination lock. Sometimes a single lock may combine some features of each, such as a Finnish combination lock whose rings must be moved to the proper position by a the turn of a key. In the United States in the 1970s, electronic locks that worked on the same principle as the touch-tone phone became popular. When the correct sequence of spring-loaded buttons was pushed, the door would open. This system used no keys, proved to be as tamper-proof as any traditional combination lock, and allowed the touch-tone sequence to be changed at any time. Magnetism has also been used to operate a Yale-type lock. These locks had keys with no serrations but rather contained several small magnets. Insertion of the key allowed its magnets to repel magnetized spring-loaded pins inside the lock which were raised to open it. The newest lock and key systems do not use anything recognizable as a traditional lock or key. Increasingly, today's hotels are switching to special plastic cards with magnetic strips on them. Like a key, they are inserted, but only momentarily, into a slot usually just above the doorknob. Often a small green light flickers after withdrawal, and the door opens if the doorknob is turned. These cards open the door using electronic systems.

Locks and keys may change considerably over time, but the universal human need to keep other people away from one's possessions will remain as important to future generations as it did to the ancient Egyptians.


Resources

books

Eras, Vincent J. M. Locks and Keys Throughout the Ages. Schiedam: Interbook International, 1975.

Hennessy, Thomas F. Early Locks and Lockmakers of America. Des Plaines, IL: Nickerson & Collins Pub. Co., 1976.

Hobbs, A. C. The Construction of Locks. West Orange, NJ: A. Saifer, 1982.

Roper, C. A. The Complete Book of Locks & Locksmithing. Blue Ridge Summit, PA: G/L Tab Books, 1990.


Leonard C. Bruno

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Combination lock

—One which is operated by a rotating dial by which certain numbers or letters in a particular order, after a given number of turns in the prescribed direction, are brought opposite the setting mark, after which the lock can be opened.

Cylinder

—The part of a cylinder lock that provides the security. It consists of a short cylindrical plug containing the key hole and mechanism, adjustable by the key.

Spindle

—The shaft of a knob or handle, usually square, which passes through the follower to enable the handle, when turned, to operate the spring bolt.

Tumbler

—A part to retain the bolt or provide security in certain locks. In England, this part is called a "lever."

Ward

—A fixed projection in a lock to prevent a key from entering or turning, unless it is properly shaped.

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