TMK abb. top master key

Top Master Key n. the highest level master key in a master key system

In Fundamentals of Master Keying, Jerome Andrews brings up the following point:

As you write a new TMK, how do you know that you haven’t already used it for some other job, perhaps very close to the one your (sic) doing now? How do you know that you are picking a new number, and not just remembering one from a system you worked on recently?

Potential TMK Problems

Jerome makes a very valid point. It’s not so much that you may actually re-use a TMK bitting, although that certainly is a possibility, but that a lower level key’s bitting might mirror it, or vice versa. If that were the case, or even if the keys parity patterns were the same, incidental master keys could be present between your systems.

parity pattern n. the collective description of the parities of a group of bitting positions in a two step progression, typically expressed in an even/odd sequence, e.g. EOOEEO

incidental master key n. a key cut to an unplanned shear line created when the cylinder is combinated to the top master key and a change key

In other words, a change key for Acme Warehouse might operate a door or multiple doors at Widget Industries down the street if the locksmith building both master key systems weren’t careful. Remember, it’s not likelihood, it’s liability that matters. No matter how remote the possibility may be, why not take the necessary steps to eliminate it out right?

How do you eliminate the possibility? Jerome’s solution was a ‘TMK Register’. A TMK Register tracks information such as key sections and parity patterns used across the master key systems a locksmith services. It also tracks proprietary information such as file and register/registry numbers. Locksmiths query the TMK Register when building future master key systems to make sure they aren’t replicating a bitting/parity pattern across a particular key section. By doing this, the locksmith can rest assured that incidental master keys won’t exist between their systems.

Example of a TMK Register

Jerome gives an example of a TMK Register in Fundamentals of Master Keying. It includes columns for the following information:

  • Manufacturer
  • Key Section
  • TMK Bitting
  • Parity Pattern or Angles
  • Register #
  • Location (City)
  • File #
  • Details

Jerome also included a “Legend” at the bottom of his example. This legend contains information unique to each system listed, such as use neuter bows, use original blanks only, or special authorization requirements. This legend helps provide special information as it relates to individual master key systems.

Constructing and Using A “New” TMK Register

Jerome’s example of a TMK Register is a good one and serves as the foundation of one I built. This TMK Register is available in Excel and PDF formats and is now available in our Pinning and Decoding Worksheets page under the newly constructed “Master Keying” tab.

The following columns are available for master key system information within this TMK Register:

  • Manufacturer
  • Key Section
  • Parity Pattern/Angles
  • TMK Bitting
  • Register #
  • File #
  • Notes

Manufacturer and Key Section

At the top of the TMK Register, there are labels for Manufacturer and Key Section. These labels are also present in the first two columns. Why the redundancy? The TMK Register example in Fundamentals of Master Keying groups all master key systems together in one list. If you only have a handful of systems, one list may be all you need. Once you go beyond that, however, it could become difficult to navigate or keep in order, especially if you’re handwriting the entries.

By giving a locksmith the option of listing, and thereby sorting, a TMK Register by a particular manufacturer and key section, the locksmith can choose how he/she wishes to organize their systems. If a locksmith wants the all of their systems on a single page, they can ignore the top labels. If they wish to sort by manufacturer and key section, they can ignore the first two columns.

TMK Bitting

This is very self-explanatory. This column is for the TMK bittings only.

Parity Pattern/Angles

There are 16 rows available for master key system entries. Assuming even-odd parity only, a 5 pin blank has 32 possible parity patterns (2^5), a 6 pin blank has 64 (2^6). This means to fully generate a parity pattern for a key section using even-odd parity you need only 2 to 4 pages, depending on the blank type. Even-odd parity isn’t the only parity pattern to you though. You could also list angles, such as for Medeco, or even polarity, such as for MIWA.

Register and File #

The “Register #” column is for the reference number that you typically assign to an entire master key system. You may not use a Register # at your shop or you may call it something else. Whatever the case, you can either remove this column or choose to ignore it.

The “File #” is for your storing/sorting systems. Maybe you label systems by account number, customer name, etc. Whatever the case, the “File #” column is to help you determine where to locate the master key file associated with a particular TMK Bitting.


I’ve included a “Notes” column and a “Notes” section at the bottom. This allows a locksmith to create his/her own legend, abbreviations, symbols, etc. The “Notes” section at the bottom contains 8 lines for text which, hopefully, is enough room to cover any necessary information as it relates to the 16 master key systems on the same page.


Here is an example of the TMK Register being utilized with all master key systems:

And here is one restricted to manufacturer and key section:

As you can see, you can build out every possible parity pattern using this approach and then input TMK bitting/systems as you use them.


Obviously a TMK Register is a highly sensitive document. As such, Jerome notes that this document should be highly secured and basic security perimeters should be followed. For example, the TMK Register should not be stored in a desk drawer or on an unlocked computer’s desktop. If printed, the TMK Register should be stored in a safe or vault on site. If digital, the file should password protected and encrypted.

Furthermore, the file itself should not include customer name and addresses. In the event that the TMK Registry were stolen it’s information should be as nondescript as possible. If you really wanted to protect a TMK Register, in addition to the recommendations previously made, you could implement a cipher to further encrypt the information. The late Don O’Shall wrote an excellent book on the subject called “Cryptography for Locksmiths” if you are inclined to go this route.

Alterations and Alternatives

We have made the document available in the Excel format which means that you can add to, remove from, and change any information you wish to suite your needs. This TMK Register is simply a guide of what myself and others use. It’s not a “one size fits all” solution, however, so feel free to craft it to your needs.

If you use software for master keying, your software may already have a TMK Register function of sorts. The newest version of MasterKing, for example, allows a TMK search. Is this analogous? To some perhaps, but not me. I believe that no matter how you create master key systems a TMK Register, when properly utilized and secured, is an effective and worthwhile supplement.