Why Do House Keys Have Jagged Teeth?
House keys turn up in pockets and keychains every day. Their jagged teeth slide into locks without much thought, yet this shape serves a specific mechanical purpose.
These teeth enable the key to operate the most common type of door lock.
The Pin Tumbler Lock Mechanism
Inside a pin tumbler lock, spring-loaded pins of different lengths sit in the cylinder. Without the correct key, the pins block rotation at the shear line. The key's jagged teeth, cut to precise depths called bittings, lift each pin exactly to align with the shear line.
Historical Origins
Pin tumbler designs date to ancient Egypt around 4000 years ago with wooden versions. The modern metal version with a flat serrated key came from Linus Yale Sr. in 1848 and his son Linus Yale Jr.'s 1861 patent, making locks smaller and more practical.
The jagged shape allows individual control of multiple pins, typically five or six, for secure operation.
In summary, house keys have jagged teeth to precisely align lock pins at the shear line, a design refined over centuries for reliable security in everyday locks.