Size: External impeller overall diameter 60 mm (2.36 in). Internal shaft insert diameter 22.2 mm (0.87 in).Replaces: Mercury 47-89984, 47-65960; Chrysler 47-803631T; Sierra 18-3017.Compatibility: For use on MerCruiser MC-I, R, MR, Alpha One sterndrives (1963-1990) and Optimax 2.5L Non-Pro models (serial number 1B227000 and above).Note: Please verify your exact HP, serial number range and motor year uses one of the part numbers above before ordering, as many look similar.Applications and use scenarios:- Replace a worn or failing impeller on an older MerCruiser sterndrive to restore proper cooling and prevent engine overheating.- Maintain a mixed fleet of boats by using a common cross-ref replacement that covers Mercury, Chrysler, and Sierra references with compatible dimensions.- Service Optimax 2.5L Non-Pro engines with serial numbers 1B227000 and above to ensure continued cooling performance.