When a landlord owns a house with several rented apartments he usually wants to have a master key that will let him enter each apartment in case of an emergency such as fire, or water pipe breakage. However, he does not want the locks set up alike so that each tenant can open his neighbour's door. When cylinder locks meet the landlord's needs in this way they are said to be set up under a master key system.
The whole secret of master keying is this: Each mastered cylinder contains not only a set of upper and lower pins, but also a middle set of pins which line up at the shear line, (the point where a lock’s bottom pin has been raised to the correct position to allow the lock plug to rotate within the lock cylinder) when the master key is inserted.
It is not always necessary to have a master pin in every pin chamber. Master pins are only used in those chambers where the master key fails to raise the lower pins to the shear line.
A master key system is created by scientific, mathematical formulas that provide an orderly progression of key cut combinations to prevent the interchange of keys, ensure accuracy and provide smooth dependable operation.
A master key rank is referred to as that following:
CHANGE KEY: A key which operates only one cylinder or a group of keyed alike cylinders in a master key system. The lock that the change key opens will also open with the use of a master key above that rank.
MASTER KEY: A key which operates all master keyed locks or cylinders in a group. Each lock or cylinder usually operated by its own change key .
The name of that system will be a master key system. ( MK ) . In some systems this will be the highest ranking key.
GRAND MASTER KEY: The key which operates 2 or more separate groups of locks which are each operated by a different master key .
The name of that system will be a grand master key system. ( GMK )
This key will operate every master system under it, and subsequent change keys under those systems.
GREAT GRAND MASTER KEY: The key which operates 2 or more separate groups of locks which are each operated by a different grand master key .
The name of that system will be a great grand master key system. ( GGMK ) .
You can go on and on with this system and make it more accessible to more groups of locks and keys .
Many master key systems consist of restricted keys, which incorporate a design registered keyway that provides legal protection against unauthorised duplication of keys. The Guild 7 restricted key system incorporating LG7 profiles are restricted to authorised members of The Locksmiths Guild of Australia.
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