What is Keyed Alike Rate and Its Significance in Locks?

In the world of lock manufacturing, the concept of "keyed alike rate" holds great importance. The keyed alike rate varies depending on the intended use of locks and adheres to specific national standards. These standards can range from a few percent to a fraction of a percent, a thousandth, or even lower, depending on the variation in security requirements.

When producing anti-theft door locks, manufacturers, based on machining precision and the number of pins, possess the knowledge of the maximum possible combinations within a lock batch. Locks are then continuously manufactured based on these permutations. The keyed alike rate represents the percentage of locks within the same production batch that can be opened by a certain number of attempts within a designated timeframe (the ratio of successful openings to the total number of trials).

The lower the keyed alike rate for a specific lock, the stronger its security and reliability. Reputable lock brands maintain exceptionally low-keyed alike rates, sometimes as low as a fraction of a thousandth. Conversely, less reputable or unscrupulous manufacturers may have higher keyed alike rates, indicating that they may employ only a limited set of lock molds for production.

Presently, national standards categorize anti-theft door lock cores into three levels: A-level, B-level, and Super B-level. According to the respective national standards, A-level locks should have a keyed alike rate of ≤0.03%, indicating that only three out of ten thousand locks are identical. For B-level locks, the keyed alike rate is ≤0.01%, and for Super B-level locks, it's even lower, approximately ≤0.0004%, signifying that just four out of one million locks share the same keying.

How is the keyed alike rate of locks determined? Let's first examine the structure of the most common pin tumbler lock:

The underlying principle is relatively straightforward. The lock in question comprises five pairs of pins – five top pins and five bottom pins – situated in corresponding pin chambers. When the correct key is inserted, the five top pins retract from the lock core into the lock body, aligning perfectly with the contact surface between the lock core and the lock body. At this juncture, turning the key activates the lock core, enabling it to unlock. Conversely, if the key doesn't align correctly, the pins become wedged at the interface between the core and the body, preventing the key from turning.

The number of potential key bitting patterns for a specific lock is governed by two primary factors: the number of pin chambers and the variety of pin tumbler lengths. As previously discussed, the number of pin chambers is a known variable. The diversity of pin tumbler lengths pertains to the different lengths available (the sum of top and bottom pin tumbler lengths remains constant). These lengths aren't arbitrary but rather possess specific gradations, facilitating the calculation of unique key bitting patterns.

For instance, with four pin chambers and five pin tumbler lengths, there are 5^4 = 625 conceivable key bitting patterns. Alternatively, in cases of six pin chambers and five pin tumbler lengths, the number of potential patterns rises to 5^6 = 15,625. However, real-world production often generates fewer patterns than the theoretical value, as certain special bitting patterns are excluded.

The greater the number of conceivable key bitting patterns, the lower the keyed alike rate naturally becomes.