flat washers. Take some 1/4 inch bronze rod and tap the end for the same thread as the sink stud. Cut the rod off long enough to reach up to the sink stud. Solder the washer to the threaded end of the rod. Cut a screwdriver slot in the other end of the rod. You just made yourself a really long nut that you can reach from the bottom of the sink. While you are at it, install a terminal board for the wires.