Locks Come In All Shapes And Sizes

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Locks come in all shapes and sizes, with many creative design variations. You can get a clear idea of the lock by examining one simple, representative lock. Most locks are based on fairly similar concepts.
Think about the normal dead-bolt lock you might find on a front door. In this sort of lock, a movable bolt or latch is embedded in the door so it can be extended out the side. This bolt is lined up with a notch in the frame. When you turn the lock, the bolt extends into the notch in the frame, so the door can't move. When you retract the bolt, the door moves freely.
The lock's only job is to make it simple for someone with a key to move the bolt but difficult for someone without a key to move it. This is put to work in a cylinder lock.

The most common lock design is the cylinder lock. In the cylinder lock, the key turns a cylinder or plug which turns an attached cam. When the plug is turned one way, the cam pulls in on the bolt and the door can open. When the plug turns the other way, the cam releases the bolt and the spring snaps it into place so the door cannot open. In a deadbolt lock, there is no spring mechanism -- the turning cylinder slides the bolt forward and backward. A deadbolt is more secure than a spring-driven latch since it's much harder to push the bolt in from the side of the door.
Inside a cylinder lock, there is a sort of puzzle, which only the correct key can solve. The main variation in lock designs is the nature of this puzzle. One of the most common puzzles is the pin-and-tumbler design.
The main components in the pin-and-tumbler design are a series of small pins of varying length. The pins are divided up into pairs. Each pair rests in a shaft running through the central cylinder plug and into the housing around the plug. Springs at the top of the shafts keep the pin pairs in position in the plug. When no key is inserted, the bottom pin in each pair is completely inside the plug, while the upper pi...