Key Cutting and Duplication: Pattern Keys, Codes, and Blanks

Duplicate vs. Code Key

The Professional Locksmith Dictionary from the Lock Industry Standards and Training (LIST) Council separates the two methods clearly.

Duplication copies a pattern key.

• A duplicate key is "any key reproduced from a pattern key."
• A pattern key is either an original kept on file for making more copies, or "any key which is used in a key duplicating machine to create a duplicate key."
• A key duplicating machine is "designed to make copies from a pattern key." On such a machine, the guide "follows the cuts of a pattern key or template during duplication."

Code cutting starts from numbers instead of a key.

• A code key is "a key cut to a specific code rather than duplicated from a pattern key," and "it may or may not conform to the lock manufacturer's specifications."
• A code original key is a code key "which conforms to the lock manufacturer's specifications."
• A key coding machine is "designed for the production of code keys." It may or may not also duplicate.

The dictionary also names how far a key sits from the factory:

• A factory original key is "the cut key furnished by the lock manufacturer."
• A first generation duplicate is a key duplicated using a factory original or a code original as its pattern.
• A first key is "any key produced without the use of a pattern key."

A duplicate can only be as accurate as the key it copies. A code key is cut to the specification itself.

What a Key Encodes: Bitting, Depth, and Spacing

ANSI/BHMA A156.5 and the LIST dictionary both define bitting as "the number(s) which represent(s) the dimensions of the key" and "the actual cut(s) or combination of a key." The parts of that combination have their own terms:

• Bitting depth: "the depth of a cut which is made into the blade of a key."
• Spacing: the dimensions "from the stop to the center of the first cut and/or to the centers of successive cuts."
• Stop: the reference point for spacing. It may be a shoulder near the bow or a tip stop at the end of the blade.
• Cut root: the bottom of a cut. Its cut root shape may be flat, radiused, or a perfect V.

As Locksmith Ledger explains, code machines use settable depth and space positions so that a key comes out with "the general cut contour equal to an original factory-cut key." Ledger adds that the industry has reached "a general agreement on measurements for almost all known individual types of keys." Each lock design also has a maximum adjacent cut (MAC) rule, which limits how different neighboring cuts can be. Ledger notes that published code series already leave out combinations that would break it. For how combinations are written and read, see key bitting.

Key Codes

A key code is a reference that leads to a bitting. The LIST dictionary defines two kinds:

• A direct code "includes the actual combination of the key."
• A blind code (also called an indirect code) is "a designation, unrelated to the bitting, assigned to a particular key combination for future reference when additional keys or cylinders may be needed."

A blind code has to be looked up in a chart, so the lock's owner or the manufacturer controls who can turn it into a key. A code series is "an ordered sequence of unique codes related to specific key combinations, key sections and manufacturers."

Manufacturers often stamp codes on the lock or key. Chicago Lock, for example, says most of its locks have a key code "stamped directly on the face of the lock cylinder or on the original key." How tightly those codes are guarded is a matter of policy. In Chicago Lock Co. v. Fanberg (9th Cir. 1982), the company kept its serial-number-to-code records secret and sold duplicate Ace keys only to the recorded owner. The appeals court still held that a published compilation of codes, gathered by locksmiths from locks they had serviced, had not been obtained by "improper means" under trade secret law. See tubular locks and key control.

Blanks and Keyways

A cut key starts as a key blank: in the LIST definition, material "manufactured to the proper size and configuration which allows its entry into the keyway of a specific locking device," not yet cut. Two shapes must match:

• Keyway: the opening in the plug, shaped to accept the right blade.
• Key section: "the exact cross sectional configuration of a key blade as viewed from the bow toward the tip."

The LIST dictionary notes that these are not necessarily identical.

Blank directories exist because the variety is large. Kaba Ilco's Key Blank Directory organizes blanks by section (vehicle, North American cylinder, international cylinder, and others). It advises locksmiths to check a selected blank "against the original Key for blade length, width, shape and milling before duplicating."

Some systems use blanks that common machines handle poorly. Locksmith Ledger explains that small format interchangeable core keyways are too small for standard blanks such as Y1, KW1, or SC1. Some of these blanks also have such thin cross-sections that they can flex in a standard vise and come out cut out of tolerance. See key blanks and keyways and interchangeable cores.

Open and Restricted Keyways

The keyway also decides who can get blanks. Schlage's L Series catalog makes the contrast explicit:

• Its Classic keyway is an "open keyway," and keys "are duplicated and available without ordering formalities."
• Its Primus cylinders use side bit milling that, in Schlage's words, "makes unauthorized duplication highly enforceable."

"Do Not Duplicate" stamps are a separate matter. They are a marking, and the Fanberg case shows that Chicago Lock used one on Ace keys. What legal force such a stamp has depends on the jurisdiction and is outside this article. See restricted keyways and high-security locks.

Machines and Their History

The LIST dictionary defines a key machine as "any machine designed to cut keys." Its cutter "makes the cuts into the key blank," and a slotter is a cutter that makes rectangular cuts. A depth key set has one key for each depth, each cut with the correct spacing. It lets a duplicating machine produce a code original key.

Locksmith Ledger's industry history gives a few milestones:

• 1927: the Ilco Universal Code Machine is invented.
• 1967 model year: General Motors adds a fifth depth and a new code series, which changed code machines and try-out keys.
• 1970s: Frank Agius, Bill Reed, and Wiggy Jensen compiled depth and space data for popular manufacturers, and Jensen, Framon, and LaGard introduced key code cutting machines.

Not every key is cut on its edge. The LIST dictionary defines a dimple key as one whose cuts "are drilled or milled into its blade surfaces." Tubular keys carry their cuts around the end of a round blade. Electronic transponder keys add a chip that must be programmed separately from the mechanical cut.

Related Topics

• Key bitting: how combinations are written
• Key blanks and keyways
• Restricted keyways and key control
• Interchangeable cores
• Tubular locks and dimple locks
• Transponder keys and smart keys
• Master keying
• Pin tumbler locks

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