Top 10 Common Terms Used In Master Key Systems

Master key systems and the locksmithing industry frequently use some terms which may not be completely understood at first. Here we’ll provide a list of common terms and their definitions surrounding master key systems.

Terms Used In Master Key Systems


Differs stands for ‘different combinations’, or in other words, combinations, permutations or sequences. This number is a factor of the design of the key, the number of locking components, the number of available positions for each component, and the tolerances of the lock.

Euro Cylinder Locks

Euro cylinder locks are the single most common profile design for locks in the world. They come in various configurations, where you can have key operation on both sides of the lock or on one side and a thumb-turn on the other side, for example.

Grand Master Key

The grand master key refers to the top-level key, above even other master keys used in the system. While there may be lower branches of a master key which open an entire subset of locks, the grand master key can open all of the locks which lower master keys can open too.

House in Multiple Ocupation (HMO)

A house in multiple occupation, or HMO, refers to a residence in which multiple occupants reside and share communal areas. Commonly managed by a landlord or letting agency. A HMO could be likened to a house share, in which the residents may not know each other prior to living together. This living situation is the perfect setting for a master key system, whereby the occupants could benefit from having one key which allows access to the property but also provides access to an individual's room and no other occupants room.

Keyed Alike

Keyed alike is a term which means that one key fits all locks. Having all doors, or some doors, keyed alike, can be beneficial for a number of reasons. Not least, the fact that you can open a set of doors with only one key.

Keyed to Differ

Keyed to differ offers the exact opposite of keyed alike. When the locks are keyed to differ, that means that you need a separate key for each lock in the system. That means more keys, but generally higher security and a more controlled access system.

Master Key

As you might expect, the master key simply refers to a single key that can open a multitude of locks within the system.

Traditional Cylinder Locks

A traditional cylinder lock is also known as a pin tumbler, as it functions based on a number of internal pins where the grooves line the pins up on what is known as the shear line. The shear line is the point at which the key inside the plug is allowed to rotate within the lock.

Master Key System

A master key system is a mechanical access system whereby a single key can open every lock in the system within a complex or business. Master key systems offer multi-level access in which the lower-level keys may only have access to one lock, the next level up could access a group of locks in the system and the highest level may have access to all of the locks. Master key systems are commonly used in a wide variety of public complexes and residential properties.

For a more comprehensive explanation of what a master key system is, you can read an in depth guide here.


This is a standard created by the British Standards Institution, in response to attacks on cylinders on doors. To meet the TS007 standard, the lock must feature a cylinder or combination of cylinder and door furniture with an accumulative 3-star rating. Locks which meet the TS007 standard compliment the security of a master key system.


These common terms are widely used in the locksmithing industry. The integration of a master key system can benefit many different settings; from residential properties to commercial properties and places of education. For more information on how your property could benefit from the integration of a master key system, contact Master Key Systems today by calling 01902 737 672 or by emailing

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