Skin Fittings/Stop Cocks - What thread?

[Wideocean7]

Hi All. I posted a few months ago about backing plates when replacing through-hull fittings. I've figured that out and thanks very much to all who contributed.

I'll be slipping my aluminium yacht in a month or so. I'll have a reasonable but rigid 3 weeks to do what I need to when she's out of the water, so am trying to get all the new bits delivered ready for installation.

The yacht was built in Canada and I think still has the original through-hull fittings and stop-cocks. Only one (a stop-cock) has an old label "Marelon 11/2") on it.

As much as I understand, there are two types of threads. British Standard Pipe (BSP) or US National Pipe Thread (NPT) either tapered or un-tapered.

My question is, how can I identity what thread the existing fittings have so I can order replacement fittings? Needless to say, I can't remove them yet as they are below the waterline!

Cheers Wideocean7