In a shaft-hub connection, what is the primary role of a key?

• A. To transmit torque between shaft and hub
• B. To center the shaft in the bearing
• C. To seal the hub from leakage
• D. To reduce noise of the connection

Answer: (A)

The main idea is how a key enables power transfer in a shaft-hub connection. A key sits in matching slots on the shaft and inside the hub, locking the two parts together so that when the shaft turns, the hub turns with it. This prevents relative rotation and allows the torque generated by the shaft to be transmitted through the connection. Without a key, the hub could slip on the shaft and torque would not be effectively carried.

Centering the shaft in the bearing is achieved by the bearing fit and the mounting of the assembly, not by the key. Sealing the hub to prevent leakage is about seals and housing design, not torque transmission. Reducing noise relates to proper alignment, fit, lubrication, and tolerances, rather than the key’s primary function.