The primary use of the G410 Mount Gasket is for galvanic insulators to separate the Stainless-Steel mounts and boating accessories from Aluminum gunwales. Without the gasket, corrosion may occur due to the dissimilar metals. Sold in pairs for installation on both top and bottom surface, and have small protrusions that isolate the mounting bolts from the aluminum as well.  The gaskets are NOT necessary for fiberglass or wood gunwales. Includes 2 mount gasket per package.