Used on many Mercruiser stern drive V8 engines. (Some V6 that came with the two piece maniflold/elbow) Note: These will Not work on V6 engines that came with the one piece manifolds (use 807166A2 it has a flat tip) ,or early V8 with the pin going through flapper. For 1998 and newer engines, there are some 1996 and 1997 models that apply. There will be two rectangular holes for the grommets. If your Y-pipe has round holes you need the A3 water shutters. If your Y-pipe changes size a few inches bellow the shutter you have a one piece manifold V6 Y-pipe and need shutter A2. If you have ever overheated these tend to get damaged. Sometimes you will find pieces of them in the exhaust when you remove the drive for servicing. They help keep water from entering the engine through the exhaust.