Illinois Duo

The Duo is a UL 437-rated wafer lock made by Illinois Lock Company. The Duo uses a total of 18 wafers that interface with three active bitting surfaces on the bottom, top, and side of the key. The Duo is popular in the United States in laundromats, vending machines and money containers.

Principles of Operation
The Duo functions similar to a traditional wafer locks but has some interesting differences. It uses 18 wafers, 14 of which are active. The Duo has four types of wafer: top (T), bottom (B), side (S), and profile (P). Top, bottom, and side wafers interact with their respective bitting surface on the key. Profile wafers are used to check the proper profile of the key throughout the lock, and are not moved by the key. The Duo uses five top, five bottom, four side, and four profile wafers. There are two bitting positions for top, bottom, and side wafers, giving the Duo 16,384 (25*25*24) theoretical key differs. Wafers are arranged in the plug (from front to back) as follows: (T B) (S P) (T B) (S P) (B T) (S P) (T B) (S P) (T B)

Top/bottom and side/profile wafers are always paired and share a spring. All active wafers have anti-lockpicking notches that resembles a mushroom security pin design adapted for wafers.

The key is made of nickel-silver and is non-reversible. The bow is stamped with an indirect key code.

Disassembly instructions
The Duo is relatively easy to disassemble, but extremely difficult to re-assemble because of the interaction between wafers and springs.


 * 1) Remove the cam or C-clip.
 * 2) Remove the plug.
 * 3) With no key inserted the wafers can be pushed out from the top or the bottom of the plug.

Vulnerabilities
The Duo may be vulnerable to one of more of the following:


 * Lockpicking
 * Decoding
 * Impressioning