A pin tumbler lock works by using a series of pins to prevent the lock from opening unless the correct key is inserted.
Here's a breakdown of the mechanism:
- Cylinder (Plug) and Housing (Casing): The lock contains a cylinder (also called a plug) that rotates to open the lock. This cylinder is housed within a stationary casing.
- Pin Stacks: Between the cylinder and the housing are several vertical shafts containing pin stacks. Each stack usually has two pins: a key pin and a driver pin.
- Shear Line: The point where the cylinder and housing meet is called the shear line. The cylinder can only rotate if there are no obstructions at the shear line.
- Pins Blocking Rotation: Without a key, the pin stacks are positioned so that they cross the shear line, preventing the cylinder from turning. Specifically, the driver pins usually sit partially in the cylinder and partially in the housing.
- Key Insertion: When the correct key is inserted, its notches push each pin stack up until the gap between the key pin and the driver pin in each stack aligns exactly with the shear line.
- Rotation Enabled: With all pin stacks correctly aligned at the shear line, there are no obstructions, and the cylinder is free to rotate.
- Locking: When the key is removed, springs push the driver pins back down, causing them to re-enter the cylinder and once again block rotation at the shear line.
In essence, the key's unique pattern aligns the pins at the shear line, allowing the lock to open. If the wrong key is used, the pins will not align correctly, and the lock will remain secured.
