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National Pipe Tapered (NPT) vs National Pipe Straight (NPS)

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National Pipe Tapered (NPT) vs National Pipe Straight (NPS)

You know the old saying: “You learn something new every day”? That proved true today as I learned what NPT actually stands for. Since I got involved in the Sanitary Fittings business I have referred to NPT as National Pipe Thread. Turns out I’ve been wrong this whole time…sort of.

You see, NPT is both a specific type of threading style and a commonly used classification for all threaded fittings within the American National Pipe Standard. The American National Pipe Standard is the national technical standard for all threads used on threaded pipes and fittings here within the United States. This standard is different to both thread size and angle found in its European counterpart the British Pipe Standard (BSP).

Within the American National Pipe standard, there are unique sub-categories including National Pipe Tapered(NPT) and National Pipe Straight (NPS).

Did you catch that? Within the category of National Pipe Thread (NPT) there is a sub-category National Pipe Tapered (another, different NPT).

So what is the difference between National Pipe Tapered (NPT) and National Pipe Straight (NPS)? Thankfully, this is straightforward (pun intended). The tapered version has a thread that when viewed from the side is tapered whereas the straight version is not. The benefit of utilizing the tapered version is that in most cases the tapered version can be secured without the need for tightening tools beyond hand strength and plumbing tape.

Visual Difference between NPT and NPS

National Pipe Tapered Profile
National Pipe Tapered (NPT)
National Pipe Straight Profile
National Pipe Straight (NPS)

In the case of sanitary fittings, hand tightening of fittings is preferred for two reasons. One, hand tools such as pliers or wrenches can cause unsightly scratches to fittings. The ease of being able to tighten these fittings without the use of tools also makes assembly and disassembly a quicker process.

National Pipe Tapered and Straight threads will engage each other for maybe one or two turns before the tapering of the NPT fittings starts to get in the way. If you’re running across an instance where a male/female thread engages but only turns a little bit you are more than likely dealing with two different threading styles.

Examples of NPT fittings offered by Sanitary Fittings

Male NPT Tri-Clamp Adapter
Male NPT x Tri-Clamp Adapter

Female NPT Tri-Clamp Adapter
Female NPT x Tri-Clamp Adapter

Tri-Clamp Thermometer x NPT Adapter
Tri-Clamp Thermometer Cap

Male NPT Butt-Weld Adapter
Male NPT x Butt-Weld Adapter

Female NPT Butt-Weld Adapter
Female NPT x Tri-Clamp Adapter

How do I measure NPT Fittings?

The majority of fittings that we offer fall in the tubing world where everything is measured by the outside diameter of the tube. In the piping world, however, fittings are measured by the Inside Diameter. So if you’re looking to determine the size of your NPT fittings you’ll need to measure the inside diameter. A good way to remember this is that Pipe has an “i” in it and thus we measure by the “I”nside Diameter.

For any other questions related to NPT fittings or the rest of our product catalog, please contact us.