Centek's fiberglass thru hull is designed for marine exhaust applications. Centek Thru Hulls are constructed from compression-molded fiberglass and will not corrode like conventional fitting made from bronze or stainless steel. 5 in. Black Exhaust Thru Hull Fitting | Centek 1200338 5 in. Black Exhaust Thru Hull Fitting Accepts 5 in. ID exhaust hose Length 6.38 in. Diameter 7.50 in.