i. Depth and spacing
Keys are cut in such a way as to lift each individual pin to its correct height to unlock the lock. This combination of key cuts is called the bitting. Each manufacturer designates several properties of the bitting to create a wide variety of possible combinations while still maintaining a functional and durable key.
Each key pin can be one of a number of heights predetermined by the manufacturer for a specific lock. Though it varies from brand to brand and model to model, it is common for there to be ten possible heights of key pins. These possible heights are numbered 0 through 9, with 0 being the shortest pin and shallowest cut on the key, and 9 being the longest pin and deepest cut on the key. This is referred to as the depth of cut. It can be expressed in several ways: First, by the pin number (0, 1, 2, 3, etc.); second, by the cut depth – that is, the depth of the cut taken away from the key blank, equal to the length of the pin; third, by the root depth – that is, the depth measured from the bottom of the key blank to the top of the cut. Except the pin number, all measurements are generally given in 1000th of an inch. A digital caliper or micrometer can be used to measure these depths. They are available at your local hardware store.
Spacing is also expressed in 1000ths of an inch and are given for measurements from cut to cut – that is, the distance from the center of one cut to the center of an adjacent cut – and shoulder to first cut – that is, from the edge of the shoulder of the key to the center of the first cut (that closest to the shoulder).
MACS stands for Maximum Adjacent Cut Specification. This is a standardization that is used to insure that a key is not pinned in such a way as to prevent easy insertion or removal of they key. When the key is inserted into the lock the pins ride up and down the ramps between cuts. If the angle is too steep, the pins will be unable to ride up the ramp and the key will get jammed. To prevent this, manufacturers designate a MACS rating for each lock. This will insure that the key is able to run smoothly through the keyway without getting stuck on the ramp. The lower the MACS rating, however, the fewer possible unique combinations of keys there will be.
A MACS rating of 5 means that no two adjacent pins should be more than 5 apart in the pin number rating. This means that with a MACS rating of 5 one should never place a 3 pin beside a 9 pin. This would exceed the MACS rating for this lock and cause operation problems with the key.
The reason that MACS ratings vary from lock to lock is because depth and spacing varies from lock to lock. The greater the spacing between pins, the higher the possible MACS rating will be. When considering angle in versus angle out on adjacent key cuts, the maximum combination of these two angles will generally not exceed 90° to 120°. Any steeper than a 90° angle and the key will not pass smoothly under the pins.