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IPS and NPS abbreviations in plumbing

pyroman's picture

Some ignorance on display here, but, the abbreviations I sometimes see on plumbing items, IPS or NPS, what do they mean and why would I care? I see them sometimes on brass fittings I think, and on slip nuts and other threaded fittings.

I am wondering, what other potential abbreviations are out there regarding fittings I may not know of???

I did measure twice and cut once, and still messed it up.

(post #66415, reply #1 of 6)

NPS is National Pipe Straight, which means the threads don't taper and to seal it would need a rubber washer or O-ring to seal , think garden hose, under sink hoses or washing machine hoses. There are different types of straight threads such as NPSM (mechanical), NPSL (locknut), etc. 

NPT (Nat Pipe Taper), MPT (NPT male), FPT (NPT female) would be something that seals by virtue of the tapered threads compressing as the joint is tightened. Copper pipe and black iron pipe are the most common examples. There is also BSP (British Standard Pipe) and a whole host of other less common thread styles.

IPS? Are you sure you aren't dyslexic?! PSI maybe....LOL, I haven't heard of IPS, doesn't mean it's not out there, just haven't heard of it before.

(post #66415, reply #2 of 6)

IPS - iron pipe standard (tapered) OR Internal Pipe Swivel Connection which is straight thread.

"NPT (Nat Pipe Taper), MPT (NPT male), FPT (NPT female)"

But will be more commonly marked MIP or FIP for male or female iron pipe.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #66415, reply #4 of 6)

Thanks Bill....I was sure it was educated Troy and myself.

I did measure twice and cut once, and still messed it up.

(post #66415, reply #3 of 6)

Troy, thanks....I never paid attention to pipe threads being tapered or not, though I know I've seen tapered threads but never wondered "why." Now I know. Great explanation. This would be a good post from BT to put in FHB because I'm sure I wasn't the only one scratching my head.


I did measure twice and cut once, and still messed it up.