Everyday Objects

Why Do Keys Have Jagged Edges?

Every bump and notch on a key is a specific height — and those heights are the combination to your lock.

Quick answer

The jagged profile of a key corresponds to a row of pins inside the lock cylinder. Each pin is a small spring-loaded rod that sits at a different height depending on the key inserted. When the wrong key is inserted, the pins end up at the wrong heights and block the cylinder from rotating. When the correct key is inserted, every pin is pushed to exactly the right height — called the shear line — and the cylinder turns freely. The specific pattern of cuts on a key is essentially a mechanical password. The more possible cut depths a lock uses, the harder it is to guess or duplicate.

Each notch lifts a pin

Every cut on a key corresponds to one pin stack inside the lock cylinder.

The shear line is the key

All pins must align at the same height simultaneously. Only the right key achieves this.

More depths means more combinations

A lock with five pins and five possible cut depths has up to 3,125 possible key combinations.

Myth: the shape is just for grip

Every cut is functional. Even the bow — the part you hold — is often shaped to indicate which way to insert the key.

A Key Is a Physical Code for Pin Heights

Inside a pin tumbler lock — the most common type — there are several small shafts containing two-piece pin stacks. A spring pushes each stack downward, blocking the cylinder from turning.

When you insert a key, the cuts push each pin stack upward by a specific amount. The goal is to get every split between the upper and lower pins to land exactly at the shear line — the boundary between the rotating cylinder and the outer housing.

When all the splits align, nothing blocks the cylinder and the lock opens. Any incorrect cut leaves at least one pin crossing the shear line, keeping it locked.

Myth vs Reality

Myth

A more complicated-looking key is always more secure

People often assume a key with more jagged edges is harder to copy or pick.

Reality

Security comes from precision and the number of positions, not jaggedness

A lock with more pins and more precise cut depths is harder to pick. The visual complexity of the key is secondary.

Single-Sided vs Double-Sided Keys

Single-sided: Cuts on one edge only. Must be inserted right-side up.
Double-sided: Cuts on both edges. Can be inserted either way up.
Dimple keys: Cuts are small holes drilled into the flat face rather than the edge.
Laser-cut keys: Identical cuts on both sides of the edge. Common in newer car locks.

Note

Pin tumbler locks have a known weakness

A bump key — a specially cut key struck with a hard tap — can momentarily bounce all pins to the shear line at once, opening some locks. High-security locks use additional mechanisms to prevent this.

Quick answers

Common questions

What do the notches on a key actually do?

Each notch pushes one pin stack inside the lock to a specific height. The right key aligns all pins at the shear line so the cylinder can rotate.

Why can a copied key sometimes fail to work?

If a cut is slightly too deep or too shallow, it pushes a pin to the wrong height and the lock will not turn.

Do all keys work the same way?

Most house and padlock keys use pin tumbler locks. Car keys often use different mechanisms including transponder chips and laser-cut profiles.

How many different key combinations are possible?

It depends on the number of pins and cut depths. A five-pin lock with five depth options gives 3,125 combinations; six pins with six depths gives over 46,000.

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