Why a key breaks at the keyway, and almost never deeper
A key is brass. The pins inside the lock are harder. That is deliberate — the cheap, replaceable part is designed to wear first. But wear is not why keys snap. They snap because they were turned before they were fully inserted. Only the outermost few millimetres of the blade are in the lock, so the entire torque of your wrist lands on the thinnest step of the key, right at the face of the cylinder. That is where the break appears, over and over.
The second half of the story is why the lock felt stiff enough to need that force. A cylinder that has been fighting you — dirty, gummed up, worn — is a lock that was already asking for maintenance. Breaking the key is not bad luck. It is the lock's last available way of telling you.
Three cases, decided by one measurement
- The break is showing — you can see the metal face and it sits proud of the keyway. This is the good case. Grip it with needle-nose pliers from the sides, never clamped over the top, and pull straight out along the line of the keyway. No twisting, no wiggling.
- Flush or slightly recessed — you can see it but cannot grip it. Now you need something thin: a broken-off hacksaw or jigsaw blade with the teeth pointing back toward you, slid along the top of the keyway until the serrations catch a cut in the fragment. Then pull straight. Or a proper broken-key extractor, which is the same idea with a purpose-made barb. Three attempts, then stop.
- Fully inside — nothing visible at all. This is not a home repair. Every poke can push the fragment past another pin stack, which turns "extractable" into "the cylinder has to come apart". Stop, and call someone who has the tools and the light.
The one action that makes it worse
Everybody's instinct is to insert the other half of the key and try to turn it. Don't. It pushes the fragment inward, and inward is the one direction that matters. The same goes for sewing needles, skewers and screwdrivers: a needle is thin enough to slide past the fragment and press it down, and a screwdriver is thick enough to score the bore. The fragment is not going to be persuaded. It is going to be gripped, or it is going to be extracted by somebody with a barbed tool.
After it comes out — two things people skip
Test it before you relax. Put a spare key in and work it several times. Smooth means the cylinder survived. Grinding, sticking or a key that won't return means a pin took damage; add dry graphite and try again, and if it still binds the cylinder needs replacing. Do not reuse the broken key. It failed once at that exact point and it will fail there again. Take the two halves to a key cutter — both pieces are a perfect tooth template, which is faster, cheaper and more accurate than cutting from the lock. Keep them even if they look useless.