Master Key System Setup: How Keying Hierarchies Actually Work
A master key system is built on a principle called a keying hierarchy. At the top sits the grand master key (GMK), which operates every lock in a property. Below it, master keys (MKs) open defined zones — say, all doors on the second floor or all locks within the accounting department. Sub-master keys go one level deeper, controlling smaller clusters such as a single suite or a row of storage units. At the base are change keys (also called servant keys), which open only one specific lock. Every lock in the system is pinned to accept its own change key and any key above it in the hierarchy — a precision task performed cylinder by cylinder, pin stack by pin stack, by our technicians.
The hardware at the heart of most commercial master key setups is the mortise lock. Unlike a standard cylindrical knob-and-latch mechanism, a mortise lock body is set into a pocket routed into the door edge, integrating the latch, deadbolt, and auxiliary functions into one robust unit. Mortise lock cylinders are especially well-suited to master keying because they accept a wide range of keyway families and pin configurations, giving locksmiths the design depth needed to create large, multi-level systems without exhausting the available key combinations. When Bolt Locksmiths evaluates your property for a new system, we assess whether your existing mortise lock hardware can be re-keyed into the hierarchy or whether upgrading cylinders will give you a more secure and scalable result.
