The Medeco Biaxial uses five or six pin-tumblers that provide axial rotation to interface with a sidebar located at 3 o'clock. Pin-tumblers must be properly raised to the shear line as well as rotated so that the sidebar arms can fall into notches on the side of each pin-tumbler. Axial rotation is provided by the design of the bottom (key) pins and angled bitting cuts on the key. There are 6 depths available for pin-tumblers, allowing 7,776 (65) theoretical key differs in a five pin Biaxial (excluding the sidebar).
The main difference between the Biaxial and the Original is that Biaxial bottom pins sit before or after the center of the bitting cut. This allows for six total positions of the bottom pins, but pins use only three true gate positions. Biaxial pins have their own rotation codes:
Type Left Center Right
Fore (Biaxial) K B Q
Original L C R
Aft (Biaxial) M D S
There are 6 total positions for bottom pins, allowing 7,776 (65) and 46,656 (66) total sidebar differs in five and six pin Biaxials, respectively. True gates on the pins can only be rotated to three positions, so there are only 243 (35) and 729 (36) actual rotational differs in five and six pin Biaxials.
The Biaxial uses 2-3 mushroom top pins in each cylinder to provide manipulation resistance to traditional lockpicking. The sidebar notches on the sides of the bottom pins may also have false gates to resist manipulation by rotation.
In addition, "ARX" pins are used to protect against manipulation by rotation. ARX pins close the sidebar notches before they reach the end of the pin, making it so they cannot be grabbed by a grove grabber or another tool.
Resistance to forced entry is provided in the form of hardened steel rods and discs. In the plug rods are in the 3, 9, and 12 o'clock positions. In the cylinder, two crescent shaped discs are placed at the 12 and 3 o'clock positions to protect the pin-chambers and the sidebar. As a secondary locking mechanism, the sidebar itself also helps to protect against a variety of forced entry techniques. Bottom pins may also have a hardened steel core to resist drilling.
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