The pulley on the tow truck boom in which the cable runs is known as:

The designation of the pulley on the tow truck boom as a sheave wheel is accurate because a sheave is specifically designed to guide and support a cable or rope. In the context of towing operations, the sheave wheel enables the smooth operation of the cable as it winds and unwinds during the towing process. This design reduces wear on the cable, minimizes friction, and allows for efficient lifting and lowering of the load being towed.

Being integral to the mechanical advantage provided by the boom, the sheave wheel ensures that forces are evenly distributed along the cable, enhancing overall performance and safety. Understanding the terminology associated with this component is crucial for effective communication and operation within the towing industry, making it clear why this answer is the most technically correct among the options provided.