Sierras 18-9803 Spanner Nut Wrench removes and installs the drive shaft bearing retainer. Designed for use with Mercruiser MC-I, R-MR, Blackhawk, all Bravo, and all Alpha drive units. It is interchangeable with Mallory 9-79801, GLM 90100, and Mercruiser Stern Drive 91-17256 and 91-36235. Check manufacturer recommendations to ensure a proper fit before purchasing. Each Sierra product meets or exceeds the original equipment part it replaces.