How does a Pin Tumbler Lock work?

When you open up a lock with a key do you ever stop to think about what's going on inside? Only the correct key will open the lock. Why is that? Each key has its own unique shape. These ridges on the key have to match exactly with the lock for it to work. There are many different types of locks,

but the most common one is called a Pin Tumbler Lock. Let me show you how this works. This outside part is called the Case. The inside part is called the Plug; this is the part that turns when the correct key is put in. The opening here, is called the Keyway. On the inside, there's a few more parts.

There are several vertical shafts that go through the Case and the Plug. Each shaft has a Spring, Driver Pin, and a Key Pin. The springs press all the pins down so that they all rest on this ledge. You'll notice that the pins meet at a different level for each shaft. For the Plug to turn,

the pins must line up with the Shear line Now watch what happens when we insert the wrong key. The pins are not lined up, which means the the Plug won't rotate. When we insert the correct key, everything lines up, and the Plug turns. So we've covered the case of one key for one lock;

there's another case. Let's say there's a building, where there's a different key for each door, but there's also a key that opens every single door in the building. This is called a Master key. For the Master key to work, there must be an extra pin in at least one of the Vertical Shafts.

We call this the Master pin. Now the Plug will turn if there is a key that raises the pins either to here or to here. So here's our regular key going in;