I realize that I’m late to the party but one thing needs to be mentioned. Typical through-hull fittings are made with straight, untapered threads. Some builders or yards try to shortcut by using a valve work NPT threads. This Is dangerous practice since NPT threads are tapered and will not mate up to straight threads properly. A proper seasick has straight threads. Regards, Randy Pickelmann Cool Change-Rockland, ME Sent from my iPhone-expect typos