V-belt idler pulleys work with power transmission belts to maintain tension and position belts away from obstacles. They are often used as belt tighteners to take up belt slack and maintain consistent tension to reduce slipping and ensure proper performance of the drive system. Idlers typically spin freely on a shaft that does not transmit power and can reduce vibration and wear on the belt. Cast-iron pulleys are durable and wear resistant. Fiberglass-reinforced nylon pulleys are resistant to corrosive environments and are suitable for drive systems that require washdown.