Tom has 35+ years in the door hardware industry, 16+ years in hardware distribution, and 17+ years as a commercial locksmith.
What Is a Master Key System?
A master key system is a set of locks that are keyed so that they each may have an individual key, called a passkey, yet all are opened by an additional, special key called a master key. These locks would be described as keyed different and master keyed.
Within a master key system, groups of locks can be keyed alike so that the same key operates all locks in the group, plus all locks in the group are operated by the master key. These locks would be described as keyed alike and master keyed.
Master and Submaster Keys
Under the master, groups of locks can be keyed differently, keyed to a submaster, and keyed to the master. For example, you might have three buildings. Each building has six locks keyed differently and a submaster key that operates all the locks within a single building. The master key opens all the locks in all three buildings, but the submaster from one building will not open any lock in either of the other two buildings.
Grand Master Keys
A grand master key might be necessary if a property manager is responsible for groups of buildings, for example. Each group of buildings would be under a separate master key; each building would have a submaster key, and then the grand master key would open everything.
The Importance of Planning Your System
The weakness of a master key system is in the key control. If the wrong person gets a copy of the grand master key, every lock in the system may have to be changed.
The way a master key system is laid out determines the ability that each individual key holder may have to operate any given lock. Therefore it is best to have a clear idea of who needs to get in where before you start.
Identify the Doors
If your master key system is going to be part of new construction, use the door numbers from the architect's hardware schedule to identify the doors. If this is an existing facility, you can assign names or numbers to the doors as you see fit.
The point of this is to be able to match up a key with a door in the future so that you will be able to look at your keying schedule and identify what keys open which door.
It's good to apply actual labels or names to the doors to avoid future confusion. Place the door number label on the door frame on the hinge side so that it is only visible when the door is open. The photo above shows the height at which door numbers are generally placed. The photo below shows how to view the applied door number with the door open.
Identify the Keys
Typically, locksmiths number keys in a master key system similar to this:
- Grand Master: A
- Master: AA
- Submaster: AAA
- Pass or Change Key: AAA1
If there are no submasters and no grand master, the master key would simply be numbered "A" and the pass keys "A1," "A2," etc.
Example in the Photo
Above is a photo of a key that is part of a master key system. Notice the number: "2818AA"
This would indicate to me that the system has a master key numbered "A," submaster keys numbered "AA," "AB," etc., and pass keys numbered "1AA," "2AA," etc.
Submaster keys are often created to match the hierarchy of the users and/or the structure of the building. For example, a building might have five floors with a different office tenant or department on each floor. In this case, one might assign one submaster key to each floor.
Sometimes submaster keys are created for different users. For example, maintenance people may have a submaster key that accesses utility and machine closets and building entrances only.
Using a Spreadsheet to Design Your System
Once you have identified your doors and settled on a key numbering system and how you are going to organize it, you are ready to design your master key system. At this stage, a spreadsheet, as shown below, can be a very helpful graphic organizer for your system.
In the above partial spreadsheet, key numbers are input across the top and door numbers are indicated down the left side. We see that the master, key number "A", opens all doors in the system. The "AA" submaster will open all doors except the Janitor's Closet and the Electrical Room. The "AB" submaster opens only the Janitors Closet, the Lab, and the Electrical Room. Key number "AA1" opens only the Office Entrance, etc.
Once you have added all doors and keys to the spreadsheet, you are ready to speak intelligently with your locksmith about how you need your system to work.
If you have any questions, please comment and I will respond.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: How should I go about developing the bitting codes to be used in my system?
Answer: These days locksmiths use master keying software to create master key systems in a flash, and it is a good way because the software seems to never make any errors. And errors are easy to make.
When I made master key systems using a paper and pencil, I started with the master key bitting. The trick is to always be conscious of the incidental bittings one creates during the process. For example, say you make a very small master key system:
Master Key A: 52531
Key number A1: 54215
Key number A2: 55967
In this small system, if I were to add bitting 55537, it would also open the lock keyed to A2. That's called cross keying, and it results from individual digits within the bitting matching either the master key or an operating key. In this case, one could change the bitting to 55533 and solve the problem.
I used to do fairly well avoiding cross keying by keeping one digit the same as the master and then adding a certain number to each other digit to come up with the next change. For example, in the series above, the next change would be 56519. In some systems, having the 1 and the 9 next to each other might not work out because they are too close together; when you cut the 9 it cuts away part of where the 1 was, and now it ends up being some nonexistent bitting like 2.4 or so.
Also, one wants to avoid monotone (i.e. 55555) or ramp (i.e. 54321) bittings that are super easy to pick; also each digit of every operating key should vary from the corresponding digit in the master key by at least 2 so as to avoid the dreaded #1 master wafer that tends to drift out of place as the lock becomes worn over time.
Question: 1) Which codes make a good master key? What is your preference? 2) Do you have a good reference for the rules of binning? 3) I am finding it difficult to find well-made DND key blanks. It seems that even Ilco keys vary depending on who they farm the manufacturing to. I have noted that there is a lot of up and down play in the key when in the cylinder due to wider key grooves. Even the brass seems of cheaper quality than the ones they made in the past.
Answer: As with all keys one originates, avoid 'ramp' (like 123456) and monotone (like 222222) bittings and bittings that have extreme adjacent depths (like 190829). Grand master keys may be thinner than operating keys if there are several different keyways in the master key system, so in that case try to avoid the deepest cuts so that the key is more durable.
Manufacturer's original key blanks and cylinders are usually much better quality. Dorma Kaba Ilco is an aftermarket cylinder and key blank company that produces good quality products, but if you want to be able to use the pin size your keying kit tells you to use, you will need to use original cylinders and key blanks.
Then instead of a lot of trial-and-error guesswork, it's just a matter of putting the right pin in the right hole.
Manufacturer's original key blanks are also available pre-stamped "Do Not Duplicate," or you can buy your own hand stamp and stamp them yourself. Most if not all lock companies have gone to nickel-silver blanks instead of brass because nickel-silver is so much more durable.
Question: How do you grand master and master a lock with a tenant key?
Answer: A basic of master keying a standard pin tumbler cylinder is to add extra top pins to one or more pin stacks to create additional combinations. Each additional combination that is created will permit another key to work the lock. Simply put, if you add one top pin to one pin stack, it will create one new combination. If you add two, it will create two. If, however, you add one pin to one stack and one pin to a second stack, now there are twelve keys that will work this lock. This makes grand master keying possible, and it also makes it difficult to achieve securely.
Tom rubenoff (author) from United States on March 03, 2019:
With great power comes great responsibility. A key that opens every door is great power. Be sure you always keep it safe.
One way to do so in your case might be to give each building its own master key. So when you give out the key to a maintenance worker, your security exposure is limited to that one building. You can still have a grand master key that opens everything, but you can limit access to this key to a select few of your most trusted people.
Many times it’s best not to give out a master key when an entrance key and an apartment key will do the same job without exposing the property to a security risk.
I suggest that you have a locksmith survey the existing hardware and recommend the best way to create the master key system. The locksmith will use key system software to create a secure master key system.
An organized key storage system and key sign-out procedure can help make sure the major convenience of a master key does not become a major liability.
Benjamin Larochelle on March 03, 2019:
Great info! As a novice property manager I am thankful for the help.
I manage 14 different properties, most with multiple keys for multiple doors.
Am I kidding myself to think that I can bring order to all of them and have one master that works them all?
I know that I will probably need to convert everything to either one brand of lock or another right? ie Schlage??
I am ok with that but honestly don’t know where to start with what my master should be? Should I just pick the key with the highest numbers to building off of?
I apologize in advance for my obvious ignorance and appreciate any guidance.
Tom rubenoff (author) from United States on December 21, 2016:
Hi Mac! Number of possible changes varies widely between pinning technologies and manufacturers. Also there's a big difference between possible changes and usable changes. That's why most locksmiths use master keying software these days.
Tom rubenoff (author) from United States on December 21, 2016:
Hi Vremner, sorry I didn't see your comment before. Thanks very much. In my career I found the biggest obstacle to getting a master key system right was getting the customer to understand the concept. This article is my attempt to address that.
mac0070 on December 21, 2016:
Hi, Can you tell me How many possible change keys will be generated under a single master key only system ? (just a master key no sub masters ) Thanks Mac
vremner on December 12, 2016:
Really great hub! I http://locksmithvaughan24.ca/ have been using this techique a lot and it seems to be pretty good. When rekeying an office or similar you basically can do both ways - from bottom to top and from top to bottom. In my opinion, you hadnt covered all area to people to choose from but boy this is a good tipp. You are almost selling our knowledge
Tom rubenoff (author) from United States on October 18, 2016:
If you are talking about a relatively small system, you could create it without the use of a computer.
Create your master key and sub-master key bittings first. For example:
Master key: "A"
Sub-master key: "AA"
Now create your first change key, "AA1":
You can see that the cylinder keyed to "AA1" can be easily keyed to all three keys. The pin stacks would look like this:
1 4 1 1 6 4
3 x 7 2 2 2
2 x x 3 x x
Under the sub-master "AA" all keys will have a #4 cut at the second and sixth positions. All cylinder not under the "AA" sub-master will not have a #4 cut in either of these positions, nor will that have a #2 cut in the sixth position to ensure that no other key in the system will open these cylinders you have keyed to three levels.
Alternatively you could create a sub-master using your software by using sectional keyways. For example, using Sargent L series keyways, you could use an LD keyway for your master key and LB keyway for your sub-master key, use LB keyway for your sub-master-keyed cylinders, and LA keyway for all the other cylinders in the system. Your LB keyway sub-master will only pass the LB keyway cylinders and your LA change keys will not pass them. The LD keyway master key will pass everything. You still need to avoid cross keying, but at least folks won't be able to try their keys in the LB keyway cylinders unless they have them re-cut on an LB, LD, or LN keyway blank.
I hope you find this helpful.
David E. Gust on October 18, 2016:
How do you key 1 cylinder to 3 keys on a standard cylinder? How can I do it in the field without using a huge computer program? My program does not allow me to input the sub master that some clients want.
Tom rubenoff (author) from United States on May 15, 2012:
Sure. What did you have in mind?
Scott on May 15, 2012:
I manage some buildings and would like to have my own 4 level key code system. Can you help get started.
Tom rubenoff (author) from United States on March 25, 2012:
louromano on March 25, 2012:
Excellent hub. good info
Tom rubenoff (author) from United States on January 12, 2012:
If I keyed locks to work with the grandmaster and a pass key only, the grandmaster key being "A", I would number those pass keys A1, A2, A3, etc. This is typical key numbering used for mechanical closets, storerooms and utility closets accessible to maintenance staff only.
Wayne on January 11, 2012:
If you have a system (A Grand Master, AA thru AE masters )and need to add keys under the master only (A1-A5) would you simply create numbers for another master, not cut it and then cut keys that would be under that master and label them A1-A5?
Tom rubenoff (author) from United States on November 28, 2011:
Yes, I have, but my general experience is that building owners and facility managers may be unlikely to be able to give you the information you really need because they lack the expertise. Often, for example, they want everyone's key to work in the front door - an easy thing to accomplish, but not really advisable in a building with more than three changes in it.
The only questions building owners/managers are usually capable of answering concern who should be able to open what. Therefore the most practical way to proceed would be to ask them to list their doors and the people who need to get into them when they are locked. From that information, the locksmith can begin to create a keying schedule.
For information about door swings and lock and cylinder types, nothing really can take the place of a site survey.
All the best,
drew on November 28, 2011:
Can you tell me if you have ever run across a questionaire for use in helping clients develop a keying schedule?
I would love to be able to leave something with a building owner so they can answer simple yes/no type questions to aid in distilling their keying needs.