Lock

=Locks= A lock is a mechanical fastening device used to restrict access to an area or enclosure. A lock consists of a bolt and a cylinder. It is the duty of the lock to restrict the movement of the bolt until the cylinder has allowed the bolt to be retracted. Locks are traditionally opened by using a proper key or combination. Modern locks may incorporate various digital access control features, such as biometrics. There several major types of locks with most modern high security locks being hybrid designs.

History
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Pin-tumbler
Originally invented by the Egyptians, modernized by Linus Yale. Uses moving pins to prevent rotation of the plug.

Wafer
Wafer locks behave a lot like pin-tumbler locks, only instead of pins, they have flat disks with holes in the center. These disks are placed in grooves in a plug, on top of springs. When the lock is locked, some tumblers protrude from the plug, into a groove in the cylinder, blocking the rotation. when the correct key is inserted, the disks retract into the plug so that it can rotate.

Lever
Lever locks are operated by simultaneously raising several levers to the right height. Each lever has a gate cut in it. The bolt has a stump that goes through each gate. when locked, it the stump will be on one side of the gate; when unlocked on the other side. The key actually moves the bolt while raising the levers.

Combination
examples: safe locks with dials, cheap master locks, luggage locks, bike locks