If you haven’t already, take a moment to stop by our Key Bitting Specifications page in the Tools section. For those new to locksmithing or for those that might not understand some of the abbreviations or information listed, I’m going to take a moment to cover each item by using one of the most popular keying systems in the United States: Schlage Classic.

Throughout this article I’m going to reference information as it’s organized in our key bitting specifications. Yes, we organize information in an arbitrary manner (one we think is the most conducive), but the information we include is the same information manufacturer’s use as well; that’s where we draw our information from, after all. Also, I’m not going to focus on items like key origination options or notes – that’s self-explanatory. Finally, I’m going to define terms using The LIST Council’s Professional Locksmith Dictionary. With that said, let’s cover the information left to right, top to bottom.

Schlage Classic key bitting specification.


What’s in a Key Bitting Specification?

Not all manufacturers list the same amount of information in each of their key bitting specifications. Some manufacturers choose to share more information than others. At the very least, we’ve found that spacing and root depth information is listed by all manufacturers. Schlage, on the other hand, leaves nothing to guess work; they list just about every relevant detail necessary for generating or decoding keys and/or pins of their keying systems. Regardless of availability, all manufacturer’s key bitting specifications include the following information:

MACS, or maximum adjacent cut specification, is the maximum allowable difference between adjacent cut depths. MACS essentially tells you which cuts are allowed to be next to each other. If your MACS is 7, for example, a 2 cut can be right next to a 9 cut because when subtracting their difference, 9-2=7, it is at or below the MACS of 7. If the adjacent cuts were 1 and 9, however, their difference would be 8, which would violate MACS and therefore would not possible. In the Schlage Classic keying system, the MACS is 7.

Increment is the distance between different, successive depths. If you look at the Root Depths, or the dimension from the bottom of a cut on a key to the bottom of the blade, you’ll notice that the measurements of different, successive depths increase or decrease, depending on the order in which you read it, by .015″. This .015″ difference is the increment for Schlage Classic.

Progression is defined as a logical sequence of selecting possible key bittings, usually in numerical order from the key bitting array. That might not make sense in our context but allow me to explain. Progression relates to master keying and can be represented as either “Single Step” or “Two Step”. Differences between cuts in progressed keys can either be 1 increment (Single Step) or 2 increments (Two Step), depending on the size of the increment. Due to tolerances and the potential for key interchange and even cylinder failure, progression must match the manufacturer’s specifications. For all intents and purposes, if the increment size is less than .023″ then it is considered a two step progression, if it is more than .023″ then it is considered single step progression. Using Schlage Classic, which is a two step progression, we cannot have a difference between cuts of 1 increment in the same chamber of a master keyed cylinder or the aforementioned risk of key interchange and cylinder failure will exist. Therefore, we must have two step, or 2 increment, progression for Schlage Classic.

E.P.D., or effective plug diameter, is the dimension obtained by adding the root depth of a key cut to the length of its corresponding bottom pin which establishes a perfect shear line. E.P.D. will not necessarily be the same as the actual plug diameter.

Included Angle is a measurement from one sloping surface of a cut to the opposite surface, typically stated in degrees. If you look at the geometry of key cuts you’ll see that they look very much like a valley. Each side of the valley is what the definition refers to as a “sloping surface”. The measurement between each sloping surface is our included angle. For Schlage Classic the included angle is 100 degrees.

Root Cut, not to be confused with the cut root, refers to the measurement of the bottom of the individual cut itself. It is also sometime referred to as cut flat. Key cuts may have different cut root shapes, or the shape of the bottom of the key cut (either flat or radium or even a perfect “V”), but the bottom of the cut will always have a measurable distance. In our example, the measurement of the bottom a cut in Schlage’s Classic key bitting specification is .031″.

Spacing is can refer to two things. First, T.F.C., or To First Cut, refers to the distance between the shoulder or tip, depending on if it’s tip-to-bow or bow-to-tip, to the center of key’s first cut. B.C.C., or Between Cut Centers, is the distance between the centers of adjacent cuts. If you have a LAB Universal Pin Kit both values can be found in each manufacturer’s box. In each case, we have the full spacing information for all key bitting specifications. That includes the T.F.C. measurement, the B.C.C. measurement, and each respective available spacing measurement possible.

Finally, we include all pin segments available for a respective key bitting specification. In the case of Schlage Classic that includes bottom, master, and top pins. In other examples, such as Corbin X Class (System 70), we include bottom and master pins for both available plug diameters as well as interchangeable core top pins and build-up pins. Whatever is available for a respective key bitting specification we include, and with the manufacturer’s verbiage.

How do we use a Key Bitting Specification?

As we say on the Key Bitting Specification page, you’re only limited by your imagination with ways to utilize and “translate” the information from key bitting specifications. The following tasks can be completed, or greatly assisted, with an accurate key bitting specification:

  • Key Generation
  • Key Decoding
  • Determining Keying Systems
  • Determining Applicable Blanks
  • Cylinder Pinning
  • Cylinder Decoding
  • Master Key and Master Key System Design