I've attached two links to the fittings I'm looking to purchase online. But I don't know if they will work together.
Chrome Plated Brass Pipe Fitting, Coupling , 1/2" NPT Female
and
Moen 116651 6-Inch Straight Shower Arm, Chrome
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1The following table describe various thread standards: onestopfire.com/threads.htm – user4991 Jan 20 '12 at 20:31
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1If you can use a smaller pipe, something like this should work, amazon.com/gp/product/B0046A8F84/… although that doesnt answer your question. – fubarcrew Jan 20 '12 at 21:18
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You would need to go to a nut and bolt shop for this one.. threads are a pain in the wrist. – Piotr Kula Jan 21 '12 at 11:17
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@fubacrew I think finding a different pipe is the way to go. The one you link to looks promising. – Brian Jan 21 '12 at 13:07
According to the Googles, IPS is Iron Pipe Straight thread. It's meant to seal on a washer-shaped gasket (like the threads the hose for your toilet or faucets attach to). NPT is a tapered thread, designed to seal on the threads, which is why you put pipe tape on them - to lubricate them and help the threads deform and create a seal.
So, while having no personal experience, I would say no, they will not thread together. I've been hunting around for adapters, but don't see anything. Which is weird, because I'd think those arms would be designed to thread into a brass NPTF fitting in the wall/ceiling.
The other answer is perfectly correct regarding how IPS and NPT threads operate, and they are quite different in that respect.
But there are also some useful similarities. The actual thread specifications are very similar:
(Source: http://www.onestopfire.com/threads.htm)
IPS (also known as NPSH) is the left circled column, NPT is the right. You can see that the actual outside diameters are very close, and threads-per-inch (TPI) are the same.
Does this similarity mean you can get a liquid-tight seal screwing IPS and NPT fittings together? No, absolutely not. But it DOES mean that in some cases you can get a useful mechanical lock between the components (albeit a relatively less common scenario).
An example would be a faucet having NPT shanks which drop below the sink for water supply attachment. These can be secured to the sink using untapered nuts.
