Mounts on transom slightly above water line to provide a water exit for boats with self-bailing cockpits. Flapper valve opens outward to allow water out of boat when necessary but seals back to prevent water from entering. Acetal construction. Accommodates 3875B thru-transom thru-hull connector (screw holes must be drilled for installation). Use as a replacement valve for 3881 thru-transom scupper.Caution: Thru-hull connectors are designed for installation above the water line only.