This item is called a seacock. A proper seacock has a flange that gets bolted to or through the hull. The seacock's purpose is to provide a positive shut off from water ingress. Flanged seacocks are considerably stronger than threading an in-line valve directly onto a thru-hull and are usually made of bronze, marelon or in some cases stainless steel.


There are many different brands of marine rated seacocks from companies like Groco, Spartan, RC Marine/Forespar, Apollo and more.