|2021 - Present
The M4 (or M4) 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 four spring biased side pins that restrict movement of the sidebar until properly positioned. One of the side pins is lifted by the Shuttle Pin movable element in the key. The M4 is easily identified by the "M4" logo to the left of the keyway.
Principles of operation
The M4 uses five or six pin-tumblers that provide axial rotation to interface with a sidebar. It uses standard, mushroom, and barrel drivers.
The M4 sidebar differs from previous models because it has small grooves cut out where the side pins fit into. Once side pins are properly lifted by the correct side bitting and shuttle pin on the key, and pin tumblers are properly rotated by the correct key, the sidebar legs can interface with the gates on each pin-tumbler.
The M4 side pins are spring-biased components located to the left of the sidebar. In their default state, the side pins block the sidebar from retracting. A moveable element on the right side of the key lifts the single Lift Pin into the correct position. Side milling on the key moves the three standard side pins into the correct position. There are three different standard side pins, with true gates at different heights, and false gates.
- Original, Biaxial, and M3 sidebars are not compatible with the M4.
Add to me!
The M4 is thought to be an improvement to the M3, allowing for enhanced key control and pick resistance. Research by the locksport community has shown a picking attack is possible.