Pin tumbler lock
The
pin tumbler lock is a
lock mechanism that uses
pins of varying lengths to prevent the lock from opening without the correct
key. Pin tumblers are most commonly employed in
cylinder locks, but may also be found in tubular or radial locks.
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Without a key in the lock, the driver pins (blue) are pushed downwards, preventing the plug (yellow) from rotating. |
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When the correct key is inserted, the gaps between the key pins (red) and driver pins (blue) align with the edge of the plug (yellow). |
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With the gaps between the pins aligned with the shear line, the plug (yellow) can rotate freely. |
The basic principles of the pin tumbler lock may date as far back as
2000 BC in
Egypt; the lock consisted of a
wooden post affixed to the door, and a horizontal bolt that slid into the post. The bolt had vertical openings into which fitted a set of pins. These could be lifted, using a key, to a sufficient height to allow the bolt to move and unlock the door.
Inventor
Linus Yale, Sr. patented a cylindrical pin tumbler lock in
1848, a design which was further improved and patented by his son,
Linus Yale, Jr., in
1861. Yale, Jr.'s design is very similar to pin tumbler locks manufactured today.
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 which 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 a corresponding set of
driver pins, which are spring-loaded. Simpler 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. Sets of locks with a master key will have one set of shear points that are identical to the others in the set and one set that is unique to that specific lock.
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Tubular pin tumbler lock* --
Lock* --
Lock* --
Lock and key*
The pin tumbler invention at Yale company site
