Flat key locks, most commonly pin tumbler locks, operate by using a key with a specific set of cuts that align internal pins, allowing the lock to open.
Here's a breakdown of how they function:
- Pin Tumbler Lock Components: The core of a flat key lock is the pin tumbler mechanism. This consists of:
- Cylinder (Plug): The rotatable part of the lock, which the key is inserted into.
- Outer Casing: The stationary housing surrounding the cylinder.
- Pins: Two-part pins (driver and key pins) located within the cylinder and casing. These pins initially block the cylinder from turning.
- Springs: Springs that push the driver pins down into the cylinder.
- The Locked State: When the lock is in the locked state, the two-part pins are misaligned, with the break between the driver and key pins sitting across the shear line (the gap between the cylinder and the outer casing). This misalignment prevents the cylinder from turning.
- Key Insertion: When you insert the correct flat key, the different cuts on the key push the pins upwards.
- Pin Alignment: The correct key pushes each two-part pin up exactly the right amount so that the break between the key pin and the driver pin aligns precisely with the shear line.
- Unlocking the Mechanism: When all the pins are aligned correctly at the shear line, the cylinder is free to rotate within the casing. Turning the key rotates the cylinder, which then operates the locking mechanism (bolt or latch), allowing the door to open.
- Key Removal: When the key is removed, the springs push the driver pins back down, misaligning the pins again and locking the cylinder in place.
In summary, a flat key's unique pattern lifts the pins in a pin tumbler lock to the correct height, allowing the cylinder to turn and unlock the mechanism.
