Medeco M3

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Medeco M3

Medeco M3
Medeco M3 cylinder.jpg
Name Medeco M3
Manufacturer Medeco
Lock Type Cylinder
Lock Design Pin-tumbler, Sidebar
Year(s) Produced 2005 - Present
Patent US 6,945,082, Expired 2021
Related Locks
Medeco Original
Medeco Biaxial
Medeco Bilevel
Medeco M4

The M3 (or m3) is a UL 437 rated pin-tumbler lock made by Medeco. The pin tumblers use axial rotation to interface with a sidebar located at 3 o'clock in the plug. It also features a spring biased slider that restricts movement of the sidebar until properly positioned. The M3 is easily identified by the "m3" logo to the left of the keyway.

It is called the M3 because it is the third generation of Medeco's axial rotation system, following the Medeco Original and Medeco Biaxial designs. The M3 provides enhanced master keying capabilities when compared with previous models, but does not provide a significant security increase. The M3 slider component is also used in the Medeco Bilevel.

Principles of operation

See also Medeco Biaxial (Principles of Operation)

The M3 uses five or six pin-tumblers that provide axial rotation to interface with a sidebar. It uses standard, mushroom, and barrel drivers.

The M3 sidebar differs from previous models because it has small grooves cut out where the slider arms fit into. Functionally, it is the same as other Medeco sidebars; pin tumblers are properly rotated by the correct key and the sidebar legs can interface with the gates on each pin-tumbler.

The M3 slider is a spring-biased component located under the sidebar. In its default state, the slider arms block the sidebar from retracting. A protrusion on the right side of the key pushes the slider into the correct position and allows the sidebar to retract. Sliders and M3 keys may be master keyed to allow a variety of protrusions to properly position the slider, but the final resting position of the slider is always the same.


  • Original and Biaxial sidebars are not compatible with the M3.

Disassembly instructions

The M3 is disassembled in the same way as a normal pin-tumbler cylinder, with consideration for the sidebar and the slider. It is recommended the sidebar be removed before removing the slider.

  1. Remove the cam or C-clip.
  2. Insert the key and turn the plug 45-90 degrees.
  3. Withdraw the plug from the cylinder. (A plug follower is recommended)


  1. Remove the chamber casings and take out each pin-stack individually
  2. Remove the cam or C-clip.
  3. Withdraw the plug from the cylinder.


The M3 was initially thought of as an improvement to the Medeco Biaxial that allowed for enhanced key control and pick resistance. Continued research by the locksport community has shown a wide variety of attacks are possible, some of which are made possible by design changes in the M3 itself. The M3 may be vulnerable to one or more of the following:

  • Lockpicking
    • The M3 slider can be easily compromised with a paper clip, lockpick, or similar object. For this reason it is not considered an effective security enhancement.
    • The Medecoder tool can be used to properly rotate bottom pins once the slider has been compromised.[1]
  • Decoding
    • The Medecoder tool (among others) can be used to decode the sidebar bitting code of non-ARX pins.
  • Bypass
    • Widening of the M3 keyway to accomodate the slider allowed for various bypass attacks on M3 locks produced before 2008.
  • Key bumping[2]
  • Key simulation



  1. King, Jon. "The Medecoder".
  2. Tobias, Marc & Bluzmanis, Tobias (2008). OPEN IN THIRTY SECONDS: Cracking One of the Most Secure Locks in America. ISBN 0975947923.

See also