In
mechanical engineering, a
key is a
machine element used to connect a rotating machine element to a
shaft. The key prevents relative rotation between the two parts and may enable
torque transmission. For a key to function, the shaft and rotating machine element must have a
keyway and a
keyseat, which is a slot and pocket in which the key fits. The whole system is called a
keyed joint. A keyed joint may allow relative axial movement between the parts.