Pin Tumbler Lock - Master Keying

Master Keying

A master keyed lock is a variation of the pin tumbler lock that allows the lock to be opened with two (or more) different keys. This type is often used for doorlocks in commercial buildings with multiple tenants, such as office buildings, hotels, and storage facilities. Each tenant is given a key that only unlocks his own door, called the change key, but the second key is the master key, which unlocks all the doors, and is usually kept by the building manager, so he can enter any room in the building.

In a master keyed lock, each of the pin stacks in the lock has three pins in it instead of two. Between the driver pin and the key pin is a third pin called the spacer pin. Thus each pin line has two shear points, one where the driver and spacer pins meet, and one where the spacer and key pins meet. So the lock will open with two keys, one aligns the first set of shear points and the other aligns the second set of shear points. The locks are manufactured so one set of shear points is unique to each lock, while the second set is identical in all the locks. A more secure type of mechanism has two separate tumblers, each opened by one key.

More complicated master-key lock systems are also made, with two or more levels of master keying, so there can be subordinate master keys which open only certain subsets of the locks, and a top-level master key which opens all the locks.