Master locks function using a pin tumbler mechanism with a key difference: some pin pairs are separated by a third pin, known as a master wafer or spacer. This allows the lock to be opened by multiple keys.
Here's a breakdown:
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Standard Pin Tumbler Locks: These locks have a series of pins that must be aligned at the shear line to allow the lock to open. Each pin is split into two parts. The correct key lifts each pin pair to the precise height so that the split between the upper and lower pins lines up with the shear line of the cylinder, allowing it to turn.
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Master Locks: According to the reference, "a few of the pin pairs are separated by a third pin". This third pin is called a master wafer or spacer.
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The presence of the master wafer creates two possible positions for each of these pin stacks that will allow the lock to open.
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This enables two different keys: the master key and the change key (or subordinate key) to both successfully unlock the same lock.
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This is particularly useful in situations where hierarchical access is needed, such as in apartment buildings or businesses.
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In essence, by introducing the master wafer, master locks provide multiple valid pin configurations, thus accommodating multiple keys for the same lock.
