This Impeller has the two flat sides that will only work on the newer style brass/bronze pumps that have 6 each 6mm x 16mm bolts holding the end cover on. NOTE: If you pump has 5 each of the 5/16" bolts, it will not work. Fits: 2000 and newer Mercruiser V6 and V8 4.3L / 262ci, 5.0L / 305ci, 5.7L / 350ci , 8.1L / 496ci engines with the brass sea water pump.