- Master Lock is a company that makes locks in many shapes and sizes and is famous for its padlocks. Padlocks use a shackle that is permanently attached to the body of the lock at one end and open at the other when unlocked. The locking end of the shackle usually has a groove cut into it that engages the locking mechanism, known as the "locking dog" when inserted into the body. The "locking dog" in turn is connected to a plug or cylinder which is moved when someone unlocks the lock, retracting the "dog." A spring usually causes the shackle to spring up and open at this point. Padlocks are easy to lock, but to unlock them you usually need a key or a combination.
- Many Master Lock padlocks employ a key to unlock the mechanism. Inside the cylinder of a Master Lock key-driven padlock are two rows of pins that are connected to springs. One row of pins is the same length and the other is of varying length. When a key that has the correct pattern to make the uneven row of pins even is inserted, the springs are activated and the cylinder can be turned. By turning the cylinder, the "locking dog" is retracted from the groove in the shackle and the lock is unlocked.
- Another common form of Master Lock padlocks is the combination lock. Combination locks have discs inside called tumblers, one for each number needed to unlock the lock. Each tumbler has an indentation at the point on its edge that corresponds with the number printed on the outside dial that is needed in the combination. When all discs are aligned, a plug is released that retracts the "locking dog" from the groove of the shackle. Combination locks also contain a trip lever spring that randomly spins the discs every time the lock is locked, resetting the combination.
