ASSA Twin 6000

=ASSA Twin 6000=

The Twin (or Twin 6000) is a UL 437-rated pin-tumbler lock made by ASSA. The 6000 is part of the Twin series of locks that use pin-tumblers and a sidebar to provide two layers of security. The 6000 is the original Twin series model. Later systems made by ASSA built upon the 6000 to provide increased security against manipulation and key duplication.

The 6000 has since been superceded by other Twin series models, particularly the ASSA Twin V-10 and ASSA Twin Combi.

Principles of operation
The 6000 uses six pin-tumbler pins and five sidebar finger pins. To open the lock, all pin-tumblers must be aligned at the shear line and all finger pins must be properly aligned with the sidebar legs. Balanced pin stacks are used to resist attack from comb picks as well as reduces wear on the springs. Driver pins come in four sizes and use a modified spool design which is combined with counter-milling in the plug chambers to provide high pick resistance. There are nine depths for pin-tumblers, allowing for 531,441 (96) theoretical key differs for the pin-tumbler portion of the lock. The MACS for this lock is five depths, giving the 6000 around 160,000 real key differs. Master keying is available using traditional pin-tumbler master pins available in eight sizes.

Unlike many other sidebar locks, the Twin 6000 finger pins are identical. Cuts are made on the sidebar directly and finger pins must be raised to match these positions. All finger pins use serrations above and below the true gate to provide manipulation resistance. Rekeying of the sidebar portion of the lock is only possibly when the sidebar is physically replaced or flipped upside-down. This interaction between finger pins and sidebar gates frustrates traditional decoding attacks that attempt to measure the range of movement of the finger pins. There are five depths available for finger pins, giving the Twin 3,125 theoretical sidebar differs (55). There are 2,800 real sidebar differs, using 1400 sidebars that can be flipped in either orientation. Keys blanks are stamped with a three digit indirect sidebar bitting code and sometimes an additional two digit keyway code.

To provide resistance against destructive entry, the 6000 uses hardened steel pins in the front of the plug and near the sidebar and third and fourth pin-stacks. In addition, driver pins are made of stainless steel to frustrate drilling of the pin stacks.

Notes
 * The pin-tumbler bitting code is referred to as the system code, and the sidebar bitting code as the sidebar code.
 * Security pin design is based on a 1942 patent by Ralph Paul Crousore.

Disassembly instructions
The 6000 is disassembled in the same way as a traditional pin-tumbler cylinder. The sidebar does not cause too many problems when the plug is removed. When the key is removed from the exposed plug the finger pins will be forced out by spring pressure.

Vulnerabilities
The 6000 system may be vulnerable to one or more of the following:


 * Lockpicking
 * Impressioning
 * Decoding
 * Key bumping

Notes
 * Bumping is possible given a bump key with the correct sidebar bitting.