What is a sprocket, and how does it relate to a chain drive?

• A. A roller used to guide the belt
• B. An idler gear
• C. A bearing housing
• D. A toothed wheel that engages chain links to transmit torque; the number of teeth determines speed ratio

Answer: (D)

A sprocket is the toothed wheel in a chain drive that engages the chain links to transfer rotation and torque between shafts. As the sprocket turns, its teeth push the chain links along, so motion is conveyed from the driving shaft to the driven shaft. The number of teeth on the sprockets defines the gear ratio, which determines speed and torque: using a smaller driving sprocket with a larger driven sprocket reduces speed but increases torque, while the reverse increases speed and reduces torque. The chain’s pitch must match the sprocket teeth so the links fit properly and don’t slip. This is what sets chain drives apart from belt drives—and why the other options don’t fit, since a belt roller, an idler gear, or a bearing housing isn’t the toothed wheel that engages a chain.