Sierra 18-4457 Mercruiser Exhaust Protector Valve - Replaces 12644A1The Sierra 18-4457 Exhaust protector valve is a compounded rubber flapper valve that prevents water from entering the exhaust system. This valve is made with weather-resistant EPDM with U/V stabilizer. Includes a stainless steel clamp.Size: 4"Interchangeable with: GLM; 89250; Mallory; 9-44001; Mercruiser Stern Drive; 12644Q01; 12644A1;