What is the purpose of a key in a shaft-hub connection?

• A. It decorates the shaft
• B. It acts as a bearing
• C. It transmits torque between shaft and hub
• D. It seals lubrication

Answer: (C)

A key in a shaft-hub connection provides a positive mechanical link that transmits torque from the shaft to the hub. It sits in matching slots (keyways) milled into both parts, so when the shaft twists, the hub is forced to rotate with it. The load is carried mainly by shear in the key and by the contact between the key and the keyways, not by friction alone. This makes the drive reliable and predictable under torque.

Decorating the shaft, acting as a bearing, or sealing lubrication are not roles of the key. The key’s purpose is specifically to transfer rotational power between components and keep them from slipping.