Always use a slightly larger bit to drill the rivet than 3/16. Up to 5/16. You want to remove just the shoulder then use a 3/16 punch to push the old rivet in. What are the 'castings' you refer to? Is that the casing? They should be soft enough to remove easily but are slightly larger than 3/16. They simply keep water from coming through the center of the rivet. You may have to cut the rivet into if the old cleat broke away before you finished drilling the rivet.



I have seen screws used in place of rivets for the jib cleats, but the threads must work well with the existing 3/16 holes.