Zero master
A chamber where the change key and TMK cut at the same depth, eliminating the need for a master pin. Useful at design time, dangerous if unintentional.
A zero master is a chamber in a mastered cylinder where the change key and the TMK happen to cut at the same depth. Because both keys share that depth, there’s no need for a master pin in the chamber — only one shear-line split is required, and a single bottom-pin/driver-pin stack handles both keys.
Zero masters are used intentionally in Rotating Constant Method allocation (the chamber holding the constant has no master pin). They become a problem when they emerge unintentionally during random allocation — they reduce the cylinder’s resistance to picking and impressioning at that position, since there’s nothing protecting the shear line beyond the standard driver pin.
Why unintentional zero masters matter
A change key and a TMK that share a cut depth at one position aren’t necessarily a security issue at the system level. But they are a quality issue:
- Pickability. A skilled picker counts how many chambers in a cylinder have master pins. Fewer master pins (i.e. more zero masters) means fewer false sets, faster picking.
- Impressioning. A zero-master chamber leaves a clear, single mark when impressioned, while a mastered chamber leaves ambiguous marks that confuse the impressioner. Unintentional zero masters help the attacker.
- Predictability. If too many change keys share zero-master positions with the TMK, it leaks information about the TMK’s bitting.
How Keyzee handles zero masters
Keyzee’s hill-climber catches zero masters during phase 03 and either rewrites the change-key cut to introduce a master pin (preserving MACS), or — when intentional, as in RCM allocation — flags the zero master in the grading output so the locksmith knows it’s by design rather than accident.
Generally Keyzee tries to keep zero-master count low except where the allocation method explicitly calls for them. A grade-A system has a zero-master count consistent with its allocation method (zero or near-zero for TPP, one per change key for RCM).
Related
→ Master pin — the pin a zero master deliberately omits → Rotating Constant Method — the allocation method that uses zero masters intentionally → TMK — the key whose bitting determines where zero masters fall