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Old 07-10-2019, 00:52   #16
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Re: Water Tank Thread - Mystery

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Originally Posted by Cadence View Post
Cherp, are you sure the threads have not been loused up from the wrong fittings being used. You may wish to retap with a known thread?
That is a possibility, but as I don't know what thread it is, I can't retap.
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Old 07-10-2019, 00:54   #17
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Re: Water Tank Thread - Mystery

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Hard to believe it would not be a US thread of some type, likely female pipe thread. Use a nylon bushing and teflon tape.
I reckon it is a US thread of some type. Maybe female pipe thread. I think gauges are the only answer although I am not sure where to borrow/acquire some of those....or even if somebody hires them out.
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Old 07-10-2019, 05:40   #18
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Re: Water Tank Thread - Mystery

My gut feeling is that it is a NPT female thread and at some time in Australia, someone has forced a male BSP thread into it and being Al, has damaged the existing threads (BSP is common here).

FWIW, at least in the smaller sizes, a male NPT can be inserted into a female BSP but it is not a a good seal unless a goodly amount of sealant is used. However trying the opposite (male BSP into female NPT) does not fit and if forced, causes thread damage.
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Old 07-10-2019, 06:59   #19
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Re: Water Tank Thread - Mystery

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Hi. This is a long shot. We have a Catalina Morgan 45 from 1998, built in Florida. It has aluminium water tanks (not good) and they have a threaded fitting welded into them. I have been trying to determine what thread is used, with no success so far. It's close to one-and-a-quarter BSP ( 32 mm aperture in the fitting). Have tried BSP and one-and-a-quarter NPT but they bind up. Anybody have a clue what thread they used? SAE? Metric? Voodoo?
CaptVR here, retired marine surveyor. Instead of wasting any more time in trying to find the appropriate threaded fitting. Go to a well driller, water pump installer, etc. Most will either lend you or rent you a 1 1/4" tap, with a deposit. This tap is about $50 bucks, so expect that for the deposit. That tap, and a Cresent wrench, and a bit of cooking oil for lube, will give you a new set of threads for a water tank. Being a pipe tap is a taper thread, a bit of over tapping will not be detrimental and a new fitting will work perfectly..
Even if this is a metric or another bastard size, for whatever fitting. If a 1 1/4" fitting starts, this tap ran in around 1/2 to 3/4 of the taps threaded length would be acceptable for a water tank. Safe Sailing All, Capt. Vince Rakstis, Ret.
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Old 07-10-2019, 07:44   #20
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Re: Water Tank Thread - Mystery

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Originally Posted by Cherp View Post
That is a possibility, but as I don't know what thread it is, I can't retap.
You can retap if there is enough meat, you can't chase out the threads without knowing. Good luck I hope you find the right fitting and it's not a bastard, which I doubt.
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Old 07-10-2019, 18:47   #21
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Re: Water Tank Thread - Mystery

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That is a possibility, but as I don't know what thread it is, I can't retap.
Sure you can, what makes you think that you can't. That's the beauty of a tapered pipe thread. I've done it a hundred times over 55 years. After the re-tap, use teflon tape, note plumbers goop. Tighten down the fitting. You will not have any problems.. Your making problems that don't exist.
Iv'e built 6 boats, 2 airplanes and full refits on probably 50 boats. What I told you will work, I'm not guessing like most folks responding to your sight, I've done it...
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Old 07-10-2019, 20:00   #22
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Re: Water Tank Thread - Mystery

Send an email to Catalina and ask.
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Old 08-10-2019, 02:11   #23
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Re: Water Tank Thread - Mystery

[QUOTE=CF32907;2991779]CaptVR here, retired marine surveyor. Instead of wasting any more time in trying to find the appropriate threaded fitting. Go to a well driller, water pump installer, etc. Most will either lend you or rent you a 1 1/4" tap, with a deposit. This tap is about $50 bucks, so expect that for the deposit. That tap, and a Cresent wrench, and a bit of cooking oil for lube, will give you a new set of threads for a water tank. Being a pipe tap is a taper thread, a bit of over tapping will not be detrimental and a new fitting will work perfectly..


Will try that. I kinda like the idea of driving a new tap through it.....at least I will know what it is.
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