Why Keys Snap and What Happens Inside the Lock
Keys break for reasons that are rarely random. Brass and nickel-silver keys develop microscopic stress fractures over years of use, especially copies that were cut from worn originals. When a key is forced into a sticky mortise lock cylinder or a misaligned door knob lock that has not been serviced in years, the torque applied in that one frustrated turn is often enough to snap the blade at its narrowest point — usually right at the bow, leaving the broken section wedged in the plug. Cold weather makes this worse: the metal contracts, cylinders tighten, and the key that worked fine all summer suddenly refuses to turn smoothly in January.
Once the key breaks, the fragment typically sits in the keyway under spring pressure from the lock pins, which actually grip and hold it in place. Attempting to pull it out with needle-nose pliers, a bobby pin, or — the approach we see most often go wrong — a dab of super glue on the end of a matchstick, usually pushes the fragment deeper or damages the delicate pin stacks inside the cylinder. A damaged cylinder cannot be extracted without replacing it, turning a straightforward removal into a full lock replacement. Calling a professional first almost always saves time and money, and it is definitely the right move for any mortise lock, which has significantly more internal components than a standard pin-tumbler lock.

