Belt pulleys are grooved wheels designed to transmit rotational power via a belt to engine and accessory components. Typically constructed from metal alloys or engineered polymers, they are integral to systems like the serpentine belt, timing belt, and alternator drives. Pulley diameter directly influences gear ratios and output speed, while groove profile ensures optimal belt engagement and minimizes slippage. Variations include fixed, adjustable, and tensioner pulleys, each serving specific roles within the drive system. Precision machining of the groove and bearing surfaces is critical for efficient operation and longevity.