What is a sheave and how does it relate to pulleys?

• A. A sheave is a grooved wheel that runs a belt; pulleys are assemblies with a shell and hub; the sheave is the belt-carrying surface.
• B. A sheave is the pulley’s housing; the belt runs on a flat wheel.
• C. A pulley is a grooved wheel that carries belts; a sheave is a complete pulley assembly.
• D. A sheave is a flat disc; a pulley has a groove.

Answer: (A)

A sheave is the grooved wheel that the belt runs on inside a pulley system. In a pulley, the term refers to the wheel component that actually carries the belt, while the pulley itself is the complete assembly mounted to a shaft, including the housing, hub, and bearings that support and align the wheel. The groove in the sheave keeps the belt seated and aligned, matching the belt’s cross-section to prevent slipping and to transmit torque effectively. The belt’s contact surface is the sheave, so the pulley’s job is to provide the structure and mounting for that wheel. The other descriptions mix up parts or omit the crucial groove that interacts with the belt.