Sierras 18-9870 Sleeve Installation Tool installs the aluminum sleeve in the u-joint bellows. Designed for use in Bravo, Alpha I, Alpha Gen II, and Blackhawk drive units/outboards (all models). Interchangeable with Mallory 9-79821 and Mercury Marine 91-818162. Check manufacturer recommendations to ensure a proper fit before purchasing. Each Sierra product meets or exceeds the original equipment part it replaces.