Reduce back flow from following seas or while backing down with a simple valve. Cockpit scuppers are great for clearing the deck of excess water, but if left open, they can be a source for water to flood the deck. Perko scupper valves are a simple solution to prevent the back flow of water caused by rough seas or the stern wake while throttling down. This molded White polymer valve surface mounts to the exterior of a 1 7/8" (approximately) or smaller integrated scupper or flush through-hull assembly to prevent the back wash with a one-way Black flapper valve.Keep the deck free of unwanted water using a surface mounted Perko scupper valve assembly. Key Features Surface mounted valve to prevent back flow caused by following seas or backing down Corrosion-free White polymer construction 2 7/8" diameter flange with 1 7/8" (approximately) interior diameter opening Pre-drilled and counter-sunk for #6 screws (sold separately) Designed to work with integrated scuppers or pre-plumbed deck drains