The Sierra 18-6457 (807757T) Serpentine Belt Idler Pulley is a direct replacement for Mercury/MerCruiser 807757T and is designed for late-model GM V6 and V8 MerCruiser engines' serpentine belt drive. It features a 3-inch outside diameter and is sized for a 13/16-inch belt width, with a composite pulley construction suitable for marine use. As 18-6457, it is widely sold as the Sierra replacement for MerCruiser applications and is cross-referenced by retailers as 807757T.
