The simplest version of a master key system is one that allows each lock to be opened using one key. This master key is also known as the restricted key system that provides reliable prompt service. Each lock in the system will have its key and that key can only open that door.
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Let's suppose that this system has 10 doors. Each door will have a unique key, meaning that one key can open only one door. This is the same for all nine doors. This master key can open all 10 doors.
Master key systems are often used in commercial applications. They can grow to be very large. One example is a grandmaster key system that could contain many systems. All locks can be opened by the grand master key.
You could also group locks on different floors in the above example. One key can open all locks within the group but not the others. A special database program can be used to create large systems and keep track of keys and locks within them. This type of keying system requires special skills.
It is impossible to discuss master key systems without talking about the lock. The lock type and several pin chambers determine the maximum size of any given system. The system will be larger if there are more pin chambers than necessary.
A 7-pin chamber lock, for example, will allow you to have a larger system than the 6-pin chamber lock. This is due to the number and type of keys that can be assigned for each system.
The master key system is generally less secure the bigger it is. A lock that can only be opened with one key is the most secure. The security of a lock will decrease if more keys can be used to open it.