A set screw is often used to:

A set screw is designed specifically to secure an object in place without the need for a nut, which makes it particularly effective for applications where maintaining alignment is crucial, such as securing a pulley to a shaft. When a pulley is mounted on a shaft, it is essential that it remains tightly in place to ensure the correct transfer of rotational motion and energy from the motor through the shaft. The set screw is threaded into the side of the pulley, pressing against the shaft to lock it in position, preventing any slippage during operation.

This functionality is critical in mechanical systems where precise movement and positioning are required for optimal performance. In contrast, the alternative options, while they may involve fastening elements, do not accurately capture the specific role set screws play in conjunction with shafts and pulleys. Thus, the use of a set screw in securing a pulley effectively highlights its purpose and utility within mechanical assemblies.