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Shim a Lock Technique: When and Why to Use It in Locksmithing

When it comes to locksmithing, having a wide range of techniques at your disposal is crucial. One such technique is lock shimming. Let's dive into the details of when and why to use lock shims, along with a few alternatives if you find yourself in a pinch.

What is Lock Shimming?

Lock shimming is not a technique for gaining entry to a locked door. Instead, it's used once you have already accessed the back of the cylinder plug and don't have a working key. By inserting a shim between the plug and the housing, you can turn the plug over, allowing you to pull it out and rekey or decode it.

Why Use Lock Shimming?

Lock shimming is favored for several reasons:

  • Non-destructive: This method does not damage any part of the lock.
  • Cost-effective: Shims are inexpensive tools.
  • Ease of Learning: It’s a straightforward technique that doesn’t take long to master.

When to Use Lock Shimming?

  • When you have access to the back of the cylinder plug: After gaining access to the lock’s internals, shimming can quickly and efficiently turn the plug.
  • Rekeying or decoding: Once the plug is turned, it can be removed for rekeying or decoding without causing any damage.

2 Types of Lock Shims

Alternatives to Lock Shimming

If you don't have a shim handy or haven’t mastered the technique, here are two main alternatives:

  1. Picking the Lock

    • Speed: Some locksmiths can pick a lock faster than they can shim it.
    • Tools: With the advent of advanced tools like leachy picks, picking has become a viable alternative.
  2. Disassembling the Lock

    • Process: Remove the top cap of the cylinder, then dump out all springs and pins.
    • Reassembly: After turning the plug, you will need to reassemble the lock, which is time-consuming and not always the best option.

Why You Might Not Use Lock Shimming

  • Lack of Tools or Experience: If you don’t have the proper tools or haven’t learned the technique, other methods like lock picking or disassembly might be necessary.
  • Preference: Some locksmiths prefer other methods due to speed or familiarity.


By following these guidelines, you'll be well on your way to mastering the lock shimming technique and knowing when and why to use it effectively in your locksmithing endeavors. Happy shimming!

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