How Many Levels Your Master Key System Actually Needs

Almost every enquiry we get about master keying opens the same way: "can you do master key?" The answer is yes, and it is not useful, because master keying is not a feature a cylinder either has or lacks. It is a plan — a map of who may open what — and the cylinders are cut afterwards to match the plan. The question that actually moves an order forward is how many levels that plan has.

The vocabulary is worth getting straight, because the abbreviations are used loosely and they are not interchangeable. A change key (CK) opens one lock and nothing else — the key a tenant or an office occupant carries. A master key (MK) opens every lock in one defined group: a floor, a wing, a department. A grand master key (GMK) opens several groups. A great grand master key (GGMK) sits above those. Between them sit the management levels a facilities team actually uses day to day — the cleaner who needs every room on two floors but no plant room, the maintenance contractor who needs plant rooms across the whole site and no offices.

We build to five levels, from GGMK down to the change key, with four tiers of management keying between the top and the individual lock. That is the ceiling, not the recommendation. Most buildings we quote need three: a change key per door, a master per floor or department, and one grand master for the building manager. Specifying five levels for a building that needs three does not add security — it adds cross-keying complexity, and every additional level narrows the number of distinct key cuts available below it.

That last point is the one most often missed, and it is arithmetic rather than opinion. A cylinder has a fixed number of pin positions and a fixed number of depths per position, so the total number of distinct keys is finite. Every master level consumes some of that space, because a master key works by adding a second shear line in the pin stack, and each added shear line reduces how many change keys can remain unique underneath. A five-level system in a small building is not more secure than a three-level one; it is a three-level building with fewer available combinations and more keys that accidentally fit more than they should.

So the design starts from the building, not from the hardware. What we need to draw a system is the door schedule with a line per door, and for each door: who must be able to open it, and which group it belongs to. That is usually a spreadsheet the facilities manager already has. From it we produce a keying chart — every door, every key that opens it, and the total key count — and that chart is what gets approved before a single cylinder is pinned.

Two practical constraints worth raising before the chart, because they change it. First, all cylinders in one system must be the same keyway, and that keyway has to be decided at the start — a system cannot be extended later with cylinders from a different profile. Second, decide early how many keys each level needs, including spares held by the building owner. Cutting additional keys to an existing system later is straightforward; discovering that the chart never allowed for the night cleaner is not.

Our cylinders are solid brass, in euro profile, in the lengths our catalogue publishes — 45, 47, 54, 56, 65, 70 and 80mm overall. That overall length is not the split: a 70mm cylinder can be 35/35, 30/40 or 40/30, and which one fits depends on your door. That is a separate decision from the keying plan and it is explained in our note on cylinder length and split, but the two arrive together on the same order, so it is worth measuring while you draw the chart.

Send the door schedule and say how many levels you think you need. If the schedule suggests fewer, we will say so — a system with one level more than the building uses is a cost and a complication that shows up years later, when somebody has to explain why a key opens a door it should not.