Mul-T Locks are produced in Israel, and are considered high security. The classic is not as secure as the later versions, though without the specialised tool or a lot of picking experience it is still difficult to open. The lock uses a “pin in pin” dimple system, that operates much like a regular dimple lock, however inside of each of the 5 pin stacks there is a seperate pin stack. Both of these must be raised to the proper level for the lock to open. As you can see, the key has cuts to bring the outer pin stacks to the correct level, as well as a small bump in the middle of the cut that raises the inner pin stack. Each pin stack is complete, with its own spring, driver, and key pin. The spring and driver pin for the inner stack is held within the outer driver pin, and the inner key pin is held inside of the outer keypin. When the correct key is inserted, the inner pins are at the same level as the outer pins, and the plug can rotate, with the wrong key all 10 pins are not aligned and the lock stays closed. Conventional picking is made more difficult because the outer stacks have to be picked before the inner stacks, and it is easy to unset an outer pin while trying to set its inner pin. A Chinese company called H&M designed and sells a tool to make picking these locks much easier, It uses a special tip to pick the pins, as well as guides and precise measurements to ensure that the tip is properly alligned over the pin stack. The classic is also vulnerable to bumping attacks, it is one of the harder locks to bump, but still possible. If you are looking for more information on other Mul-T locks, check out datagrams paper at http://lockpickingforensics.com/articles.php .