Low Key Machine

Diagram of a machine key seated in the keyway of a hub and the keyseat of a shaft

Machine Key n. — a machine element that locks a rotating part to a shaft so neither can turn without the other, carrying torque between them. It seats in slots cut to receive it: the keyway in the hub, the keyseat in the shaft. Assembled, they form a keyed joint — one that holds against rotation, yet may still let the parts slide along the shaft.