Inside a Combination Lock

Have you ever wondered what is inside a combination lock? In this article, we’ll take a look at the components and working of a combination lock!

Components of a Combination Lock

The number of combinations determines the number of wheels in the wheel pack. Each number has one wheel. When the dial is turned, the spindle engages the cam on the drive. There’s a drive pin connected to the drive cam. As the cam spins, the drive pin finally comes into contact with a small tab on the adjacent wheel called the wheel fly.

Wheels & Notches

Each wheel has a flywheel on either side of it. The drive pin rotates the first wheel until it comes into contact with the wheel adjacent to it. This keeps going until all the wheels are turning. This is called picking up the wheels. All the wheels on the spindle have a notch cut. When the correct combination is dialled, both the wheels and notches line up perfectly.


A fence is a small metal bar that is fixed to the lever. The fence stops the door from opening without the correct combination being dialled by leaning on the wheels and blocking the bolt’s path that secures the door.

When all the wheels line up, the notches align to create a gap. In a padlock, the gap allows the locking hasp to release. Under the influence of its own weight, the fence falls through the gap. With the fence gone, the bolt slip past quickly, and the safe is opened.

Using a Combination Lock

If you have used a combination lock, you know how to open it:

  • Turn the dial clockwise to two full rotations for the first number. Turn it counter-clockwise past the first digit to the second digit of the combination.
  • Turn the dial clockwise to the third digit of the combination.
  • The lock is opened.

Now you can see what happens while you rotate the dial to different numbers of the combination. Turn the knob two full revolutions through the teeth of all three cams, so the three cams turn in unison. Now, as you turn counter-clockwise, only the top cam rotates. As you move the first number, the first cam tooth triggers the second cam, so the two cams start moving simultaneously. The friction provided by the spring holds the third cam in its place. When you turn the knob clockwise again, just the top cam rotates. Once all three indentations are correctly aligned with this procedure, the lock will open.

Locksmith Kidderminster – Doctor Locks

If you are thinking of getting more sophisticated combination locks, Doctor Locks has the right expertise to help you choose the right locks without breaking your bank. Our mobile teams of experts are available round the clock through Kidderminster to provide prompt services that are insured and carried out by the ACPO policies and guidelines. Contact us today at 01562 950015 and speak to one of our engineers or reach us over email, and one of our advisors will be in touch with you soon.