The pin tumbler lock, also known as the Yale lock (after Linus Yale Jr) is a lock mechanism that uses a series of spring-loaded pins of varying lengths to prevent the lock from opening without the correct key. When the correct key is inserted the pins align precisely, allowing the plug within the lock cylinder to rotate freely, thereby unlocking the mechanism. If the wrong key is used, the pins remain misaligned, preventing the plug from turning and securing the lock against unauthorized access. It is one of the most widely used and enduring lock mechanisms in the world. Pin tumblers are most commonly employed in cylinder locks, but may also be found in tubular pin tumbler locks (also known as radial locks or ace locks).
History
The first known example of a tumbler lock is often credited to have been found in the ruins of the Palace of Khorsabad built by king Sargon II (721–705 BC.) in Iraq. There is strong linguistic evidence that pin tumbler locks exited even earlier than the regular cited Egyption invention in Mesopotamia. This is backed up by the discovery of physical artefacts at Nimrud, prior to its destruction by ISIS in 2015, and published in David and Joan Oates "Nimrud: an Assyrian Imperial City Revealed" in 2001. Further linguistic evidence comes from Dr. Karen Radner of University College London in her 2010 papers "Gatekeepers and Lock Masters: The Control of Access to Assyrian Palaces". The origins of the lock can therefore be established sometime between 2500 and 1800 BCE in Mesopotamia. A lot further back than Vivant Denon's discoveries in Egypt during Napoleon's invasion and his Corps des Savants. Such a lock, however, may be defeated by lifting the pins uniformly beyond the unlatching point. In 1805, the earliest patent for a double-acting pin tumbler lock – one where lifting the pins too much or too little prevented opening – was granted to American physician Abraham O. Stansbury in England. It was based on earlier Egyptian locks and Joseph Bramah's tubular pin tumbler lock. Two years later, Stansbury was granted a patent in the United States for his lock. In 1848, Linus Yale Sr. invented the modern pin-tumbler lock. In 1861, Linus Yale Jr., inspired by the original 1840s pin-tumbler lock designed by his father, invented and patented a smaller flat key with serrated edges, as well as pins of varying lengths within the lock itself, the same design of the pin-tumbler lock in use today.
Design
The pin tumbler is commonly used in cylinder locks. In this type of lock, an outer casing has a cylindrical hole in which the plug is housed. To open the lock, the plug must rotate. The plug has a straight-shaped slot known as the keyway at one end to allow the key to enter the plug; the other end may have a cam or lever, which activates a mechanism to retract a locking bolt. The keyway often has protruding ledges that serve to prevent the key pins from falling into the plug, and to make the lock more resistant to picking. A series of holes, typically five or six of them, are drilled vertically into the plug. These holes contain key pins of various lengths, which are rounded to permit the key to slide over them easily.
Above each key pin is one or more spring-loaded driver pins. Simple locks typically have only one driver pin for each key pin, but locks requiring multi-keyed entry, such as a group of locks having a master key, may have extra driver pins known as spacer pins. The outer casing has several vertical shafts, which hold the spring-loaded pins. When the plug and outer casing are assembled, the pins are pushed down into the plug by the springs. The point where the plug and cylinder meet is called the shear point. With a key properly cut and inserted into the groove on the end of the plug, the pins will rise causing them to align exactly at the shear point. This allows the plug to rotate, thus opening the lock. When the key is not in the lock, the pins straddle the shear point, preventing the plug from rotating.
Commonly pin tumbler locks are found in a cylinder that can be easily unscrewed by a locksmith to facilitate rekeying. The first main advantage to such a lock, also known as a profile cylinder lock or euro, is that the cylinder can be changed without altering the boltwork hardware. Removing the cylinder typically requires only loosening a set screw, then sliding the cylinder from the boltwork. The second is that it is usually possible to obtain, from various lock manufacturers, cylinders in different formats that can all be used with the same type of key. This allows the user to have keyed-alike, and master-keyed systems that incorporate a wide variety of different types of lock, such as nightlatches, deadbolts and roller door locks. Typically, commercial padlocks can also be included, although these rarely have removable cylinders. Standardised types of cylinder include:
Rim-mounted (also known as night latch) cylinders Euro cylinders Key-in-knobset cylinders Ingersoll-format cylinders American, and Scandinavian round mortise cylinders Scandinavian oval cylinders There are also standardised cross-sectional profiles for lock cylinders that may vary in length - for example to suit different door thicknesses. These profiles include the europrofile (or DIN standard), the British oval profile and the Swiss profile.
Other varieties A tubular pin tumbler lock is a pin-tumbler lock with a round keyway. A dimple lock is a pin tumbler lock where the bitting is located on the side of the key, rather than the top.
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