I am working on same issue. I am not having much luck with the square plate. It doesn"t tighten down for me. I like the flat nut idea, even though it is probably not correct. I have seen a locking washer to go into the keyway cut into the panel. But no one here is talking about it...different year maybe? Mine is a 72 Cuda. Which nut is correct? The flat one or the cone shaped one? Details Details. Thanks, Jeff