Glossary · Plain-language reference
Trade vocabulary,
in plain language.
Every term that comes up in commercial master keying — TMK, MACS, phantom keys, side bits, SFIC, the lot. Useful whether you're learning, training an apprentice, or just trying to remember what makes a master pin "thin".
- 20
- defined terms
- 4
- categories
- 11
- letters covered
- 0
- paywalled · always free
Categories
Four threads running through the trade.
Hardware describes what you hold; Keys describes what opens it; Math describes the engine; Compliance describes what you owe the customer on handover. Most jobs touch all four.
A–Z
Every term, alphabetical. Click to read the long form.
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- MACS (Maximum Adjacent Cut Specification) Math The maximum allowed difference in cut depth between two adjacent positions on a key. Mandated by the lock manufacturer.
- Master pin Hardware An extra pin between the bottom pin and the driver pin that creates a second valid shear-line split, allowing two keys to open the same cylinder.
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- Phantom key Math A combination of pin elevations that opens a cylinder it shouldn't, even though no real key was cut to that combination.
- Pin tumbler Hardware The cylinder mechanism in most modern locks: a row of spring-loaded pins that the correct key lifts to a precise height to free the rotating plug.
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- Restricted keyway Compliance A keyway whose blanks are sold only to licensed locksmiths under a controlled distribution agreement. Prevents unauthorised key duplication.
- Rotating Constant Method (RCM) Math An allocation pattern where each change key shares one position at TMK depth — the constant — and the constant rotates across keys, reducing phantom count.
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- Shear line Hardware The horizontal boundary inside a pin-tumbler cylinder where the rotating plug meets the housing. The plug rotates only when no pins cross this line.
- Side bit Hardware A cut on the side of a key blade (rather than the edge) that engages a side-bar mechanism inside the cylinder.
- Small Format Interchangeable Core (SFIC) Hardware A removable cylinder design with a control-key shear line, allowing the core to be swapped without disassembling the lockset.
See the math, then run it.
30 days, no card.
Glossary's free regardless. The engine that uses these terms is what costs A$49/mo.
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