The government will have to replace the locks on 118,000 trailers used to house the victims of Hurricane Katrina. On Monday, the Federal Emergency Management Agency announced that many of the trailers had the same "locksets," meaning they all shared the same key. Aren't all keys different?
Not by a long shot. The trailers purchased by FEMA came equipped with locks from two different manufacturers, and neither brand came with more than 200 different key configurations, or "changes." The three types of locks that were used on the trailers came with 51, 100, and 200 changes respectively. In other words, if your trailer came with the first type of lock, your key could open one out of every 51 trailers manufactured the same way.
Standard locks can only be "keyed" in a certain number of ways, depending on how they're designed. For example, the very popular, mass-produced pin-tumbler locks from Kwikset come with about 50,000 different combinations. That means if you checked enough hardware stores you could find identical, "cross-keyed" Kwikset locks.
A lock manufacturer sets the configuration of a pin-tumbler lock by inserting a set of pins of different lengths. Only a key with the right pattern of bumps will push each pin up just enough to free the cylinder and open the lock. A basic lock might have five pins, each of which could be eight different lengths. That means you'd have 85 theoretical combinations, or 32,768 changes. (In fact, not all of the combinations are usable.) You can increase the numbers by adding pins or pin lengths, or by changing the grooves that run along the side of the key. (If you want to make locks with master keys, you'll end up choosing from a smaller number of changes.)
In practice, manufacturers don't always use all the available combinations. Sometimes a customer will buy a set of locks and ask that the key changes be restricted. That means the manufacturer won't key its locks with those combinations for any other customer, thus shrinking the pool of available key types for everyone else.
Cross-keying tends to be a bigger problem with the inexpensive, lightweight locks that are built into furniture or on the door handles of RVs and trailers. To save money, a trailer manufacturer might decide to use a disc-tumbler lock instead of the pin variety. A lock-maker has less freedom to vary disc shapes than he does to change the lengths of pins, so the disc lock comes with fewer possible configurations. If a small pin tumbler could be keyed 1,000 different ways, a similarly sized disc tumbler might come in only 100 or 200.
A lock with a few hundred key changes may be appropriate for trailers that ship to all different points around the country. FEMA may have run into a problem because it ordered 150,000 trailers for the same general location, all at once.
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Explainer thanks Lou Galvao of CompX, David Lowell of the Associated Locksmiths of America, and Pat Philbin of FEMA.