Centek's fiberglass thru hull with flapper valve is designed for marine exhaust applications. 3 in. Black Exhaust Thru Hull with Flapper | Centek 1200299 Exhaust thru hull fitting For use with 3 in. inside diameter marine exhaust hose Includes rubber flapper to prevent backflow of water into the exhaust system Black color Made of compression molded fiberglass Will not corrode like metallic thru hulls 4 pre-drilled mounting holes 5 1/2 in. length 3 in. shank length 4.88 in. flange diameter Replacement flapper repair kit P/N 1200313