Key Bitting: Cut Depths, Spacing, and Key Codes

The Parts of a Key

Schlage's catalog glossary names the basic parts:

• Key blank: "an uncut key manufactured to allow its entry into the keyway of a specific cylinder."
• Blade: "the part of a key that may contain the cuts and the millings."
• Bow: "the portion of the key that serves as the grip or handle."

The bitting is cut into the blade. See key blanks and keyways for the blank itself.

The Parts of a Bitting Specification

Each manufacturer defines how its keys are cut. A Locksmith Ledger overview of code machines notes that the industry has "a general agreement on measurements for almost all known individual types of keys." The main elements:

• Spacing: where each cut sits along the blade, measured from a stop. On Schlage B and R family keys, for example, Schlage says "the stop is at the shoulder of the key." The Ledger gives typical cut-to-cut spacing of about .109–.140 inch for locks with .095-inch-diameter pin tumblers and about .150–.160 inch for .115-inch pin tumblers.
• Depth: each position can be cut to one of several depths. Depths are designated by numbers, and Allegion's published MACS examples show Schlage and Falcon depths numbered from 0 up to 9. Depth steps are separated by an increment, which Locksmith Ledger defines as "the uniform difference between successive key cuts."
• Root depth: "the dimension from the bottom of the cut to the bottom of the blade," in Locksmith Ledger's words.
• Cut angle: key cuts are V-shaped, and Allegion notes that "each manufacturer uses different measurements for the angle, depth, and spacing of their key cuts." Code machines therefore use different cutter blades for different key families.
• Recording order: bittings are written in a set direction. Schlage notes that on its B and R family keys the stop is at the shoulder "even though the bittings are read and written tip to bow." The convention has to be known to read a bitting correctly.

Specific depth and spacing tables are manufacturer data and are not reproduced here.

How Bitting Maps to Tumblers

Schlage's glossary defines a bottom pin as a tumbler "with a conical point at the end that comes in direct contact with a key." The top pin sits above it. Each cut depth corresponds to a bottom pin of matching length. When the correct key is inserted, every bottom pin rises until the gap between it and the top pin meets the shear line. Change one cut and one pin stack no longer aligns.

This is why rekeying works: changing the pins to match a new bitting retires the old key without replacing the lock. It is also why key cutting accuracy matters. The Ledger code-machine article frames the goal as a key "with the general cut contour equal to an original factory-cut key."

Maximum Adjacent Cut Specification (MACS)

Not every combination of depths can be cut. Allegion explains that MACS "refers to the maximum variance allowed between two adjacent cuts on a key." When an adjacent pair violates the rule, "some or all of the shallower cut" is removed by the cutting machine. Allegion attributes MACS to three factors, "the angle of the key cuts, the depth of the key cuts, and the spacing of the key cuts," so MACS "is not consistent from one manufacturer to another."

Allegion's published examples:

Cutting by Code

Keys do not have to be copied from another key. Schlage's catalog says its keys can be duplicated "or cut... by code," and that for some families "Standard Schlage depths and spacing are used, so there are no new settings for code machines." The Ledger describes code machines as having "settable depth and space locations." In other words, a code machine turns a written bitting and a manufacturer's specifications into cuts.

That is also why bittings and codes are protected information. BHMA's high-security cylinder standard, ANSI/BHMA A156.30 (current edition 2025), lists "key blank control" and "cylinder marking restrictions" among its key control attributes. See key control and restricted keyways.

Bitting in Master Key Systems

In a master key system, a cylinder accepts more than one bitting. Schlage defines a master pin as a tumbler "used between the bottom and top pins to create additional shear lines." A change key is "a key that operates one cylinder or a group of keyed alike cylinders in a key system," and a master key is "a key that operates all master keyed locks or cylinders in a key system or a part thereof."

Planning those combinations is a design task. BHMA publishes ANSI/BHMA A156.28-2023, Recommended Practices for Mechanical Keying Systems, and offers it free of charge. BHMA says it "covers system design," the "essential keying conference," and "good practices for effective key management."

Related Topics

• Pin tumbler locks: shear lines, key pins, and drivers
• Key cutting and duplication: code machines and accuracy
• Master keying: multiple shear lines and key hierarchies
• Rekeying locks: changing bitting without new hardware
• Key control: protecting bittings and codes
• Key blanks and keyways: the blank the bitting is cut into

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