Check out the info about marine exhaust systems on sbmar.com. If your Cummins exhaust elbow is of the same design as what mine was (original install Cummins brand), do yourself a huge favour and replace it with a custom made exhaust that will ensure that saltwater does not "back drain" into your exhaust manifold and worse yet into your engine. Big bill if that happens for any length of time. Check out the website info. By the way, I had my 'custom exhaust" made by National Marine Exhaust in Marysville, Wash. They did a good job, for less cost than a Cummins replacement.