What is the primary purpose of a key in a mechanical assembly?

• A. To enhance aesthetics
• B. To transmit rotational movement
• C. To act as a decorative element
• D. To provide flexibility

Answer: (B)

The primary purpose of a key in a mechanical assembly is to transmit rotational movement. Keys serve as a critical component in connecting rotating parts, such as a shaft and a hub. They fit into a keyway—a slot machined into the shaft and the hub—ensuring that the rotation of one part is effectively transferred to another. This mechanical connection prevents slippage and maintains a secure link between the components under operational stresses.

The other options do not align with the fundamental role of keys. While aesthetics and decorative features can sometimes be a consideration in design, they do not reflect the primary mechanical function of a key. Additionally, flexibility is not a characteristic associated with keys, as their primary role is to provide a rigid connection that facilitates the efficient transfer of motion.