Mercury - Quicksilver 816431A1 U-Joint Bellows MerCruiser Alpha One Gen II & Vazer Sterndrives 816431A1. Overview. The Quicksilver 816431A1 U-Joint Bellows keeps the heart of your drive system sealed tight. Designed for MerCruiser Alpha One Gen II (1991 and newer) and Vazer sterndrives, this flexible bellows keeps water out of the bell housing and protects the U-joints from corrosion and damage.. Made from durable, ribbed composite material, it flexes with your drive's movement while maintaining