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Old 08-01-2012, 22:06   #61
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Re: PVC Seacocks..?

Why not just run a NPT die over a NPS thru hull? Then you can make it what ever length needed. It takes very little effort since most the thread is already cut and only cutting die deep.
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Old 09-01-2012, 07:03   #62
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Re: PVC Seacocks..?

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Originally Posted by US1Fountain View Post
Why not just run a NPT die over a NPS thru hull? Then you can make it what ever length needed. It takes very little effort since most the thread is already cut and only cutting die deep.
They don't do this because it would leave too little wall thickness and the thru-hull could snap. This is why Groco used a "combination" thread that does not cut deeper into the wall thickness and only shaves the peaks of the male threads off.
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Old 09-01-2012, 15:01   #63
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Re: PVC Seacocks..?

So I understand that to say that the ID is smaller on a NPT pipe than a NPS thru hull?
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Old 09-01-2012, 16:41   #64
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Re: PVC Seacocks..?

I've measured the nominal wall thickness of a 1" Apollo/Conbraco bronze thru-hull at about 1.54mm at the threads and they are threaded the whole way. This is about the same wall thickness as a US penny.

If you feel there's enough meat there then that's your choice. The Groco engineering department has told me why they won't cut NPT threads into a bronze NPS thru-hull and why they use a combination thread instead. I then went and measured it and decided they were wise. Personally I would not want to cut one any thinner than a US penny.

I know a 3/4 Apollo/Conbraco thru-hull will fail well before the ABYC standard / 500 pound static load for 30 seconds, when it is connected to a bronze valve and loaded at the in-board end of the fitting. I would imagine it would possibly fail sooner if any thinner.
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