This is the raw water pump stop lug for many crank mounted raw water pumps. If fits between the inlet and outlet to hold the pump securely in place in conjunction with the bracket to keep the pump from coming off the engine in the event of pump or bearing failure.
The part number for this item is 3857954
Works with the following raw water pump part numbers and all their prior part numbers.
21214599
21214595
21214596
21214601
21427729
21427730