Which description best defines a sunk key?

• A. The key is helical along the shaft
• B. The keyway is cut in hub only
• C. The keyway is cut in shaft only
• D. The key is cut in both shaft and hub

Answer: (D)

A sunk key is a type of key used in mechanical couplings, where it is inserted into a keyway that is machined into both the shaft and the hub. This design allows for a secure and precise transfer of torque between the two components, ensuring that they rotate together effectively without slipping.

By having the key cut into both the shaft and the hub, the sunk key provides a fixed position for the hub on the shaft, which maintains alignment and stability during operation. This is particularly important in applications where high torque is involved, as it prevents the hub from moving independently of the shaft.

In contrast, the other options describe characteristics of different key arrangements or configurations that do not align with the definition of a sunk key, which specifically requires the key to be embedded in both components. Understanding the role and definition of a sunk key is crucial in mechanical design, as it directly affects the performance and reliability of machinery.