How does a Combination Lock work?

1. Most combination locks use what’s known as a wheel pack, which is a set of wheels that work in conjunction with each other to know the right combination; one wheel for each number. The number of wheels is determined by the amount of numbers in the combination.

2. The typical combination lock also has a combination dial that is connected to a spindle. Inside the lock, the spindle runs through the wheels and a drive cam.

3. When the dial on the lock is turned, the spindle turns the drive cam, which in turn rotates the drive pin; which makes contact with a small tab on the adjacent wheel called a wheel fly.

4. Each wheel has a wheel fly on each of its sides and a notch cut into it, so when the right combination is dialled, the wheels and the notches line up perfectly.

5. Another part of the combination lock is the fence, which is a small metal bar attached to a lever that prevents the lock from being opened without the proper combination.

6. When all the wheels in the wheel pack are in the correct position, their notches align to form a gap. Under the force of its own weight, the fence falls into the gap allowing the safe to be opened.