Seacocks have straight threads for the thru-hull to go into. On the output end they have pipe threads. Pure ball valves, which are not seacocks, have pipe threads on both ends and are NOT made to mate with thru-hull fittings. I would always use a proper seacock when attaching to a thru-hull. I have only used ball valves as what they are "valves" inside the boat AFTER the seacock.