Mercruiser Gen 4 Lifetime Series Stainless Steel Sea Water Pump Pumps are cast from 316L high quality stainless steel Uses a double roller bearing style snout assembly while integrating a one piece rear impeller housing Fits most Bravo, TR, TRS applications Replaces a sierra #18-3600 and Mercruiser 46-72774A32 and 46-807151A12.