We have listed this under catches and latches as that seems most appropriate given that we don`t really know exactly what it is ! It`s obviously something to do with trains given that it is heavily marked for the Great Western Railway Swindon. We can say that it is incredibly heavy and incredibly well made with an incredibly strong spring. It appears to be complete and we have deliberately left the wealth of surface character as found. We have lightly cleaned and polished this wonderful bronze thing, but it is otherwise in original condition. Would make a most unusual bathroom or study lock if your door and arm is strong enough.