Are you familiar with the kind of pipe thread that you need? Are you following national pipe thread standards? Did you even know that these standards exist?

If you're not sure about your pipe threads, you're not alone. Sometimes, we get so caught up in the work that we're going that we completely forget to update ourselves on the newest and best pipe threads and pie fittings.

But, as we all know, these kinds of details matter. So, that's why we're going to talk about them today.

Following these standards is important to maintaining safety and ethics in your practice. So, let's get started.

What Is the National Pipe Thread?

The national pipe thread (NPT) exists in the United States. There is a tapered (NPT) and a straight (NPS) thread. Experts use both to join pipes and fittings.

The American National Standards Institute (ANSI) and the American Society of Mechanical Engineers (ASME) composed standards for these pipes. These companies are similar in that they focus on regulations and compliance. But, they do differ in their focuses.

Regardless, they came together to form these standards based on the expertise of the ANSI and the experience of the ASME.

The standard B1.20.1 covers threads of sixty-degree form. These have flat crests and roots in a range of sizes. These start at one-sixteenth of an inch and go to twenty-four inches.

Accounting for Nominal Pipe Size

The national pipe thread (NPT) exists in the United States. There is a tapered (NPT) and a straight (NPS) thread. Experts use both to join pipes and fittings.

The American National Standards Institute (ANSI) and the American Society of Mechanical Engineers (ASME) composed standards for these pipes. These companies are similar in that they focus on regulations and compliance. But, they do differ in their focuses.

Regardless, they came together to form these standards based on the expertise of the ANSI and the experience of the ASME.

The standard B1.20.1 covers threads of sixty-degree form. These have flat crests and roots in a range of sizes. These start at one-sixteenth of an inch and go to twenty-four inches.

Common Piping

These are the most commonly-used sizes in inches:

  • One-eighth
  • One-fourth
  • Three-eighths
  • One-half
  • Three-fourths
  • One
  • One and one-fourth
  • One and one-half
  • Two

Since these are the most popular forms, suppliers in the United States have them on hand. However, you may notice smaller sizes than those we've listed if the engineer is working with compressed air.

You shouldn't see any sizes bigger than these though. It's possible, but engineers typically steer away from anything larger than two inches. This is because there are other methods that are more practical for joining pipes at greater than three inches.

Evaluating Diameters

Nominal Pipe Size relates to the inside diameter of schedule 40 piping. The pipe wall thickness affects the diameter. This causes the threads to be larger than the NPS.

Other kinds of piping may have different wall thicknesses. But, the thread profile and external diameter should remain the same. Because of this relation, the inside diameter of the pipe is going to be different from the nominal diameter.

Steel pipes with threads in a production warehouse

Threaded Pipes

It's important to evaluate the effectiveness of pipe threading for sealing purposes. An effective thread pipe can adequately seal liquids, gases, steams, and fluids.

Because these pipes are effective, experts are expanding their uses. You can find them in brass, steel, nylon, and cast iron forms. You'll even find PVC piping with these qualities. 

The taper on the threads is the key. These allow the NPT threads to form a seal when the flanks of the threads compress against one another. This happens as they're torqued.

Straight thread fittings and compression fittings are not as effective. They can't provide a good enough seal.

In fact, you may be able to see the clearance between the crests and the roots of the threads. This is where leakage can (and probably will) occur.

The problem is one of the reasons why we prefer using NPT fittings that are leak-free. They may have thread seal tape or a thread sealant compound that can help to make sure that no material will leak out.

You may have also heard of Dryseal (NPFT). This provides better leak-free protection without having to use tape or another sealant. NPFT threads appear similar to other standard pipes.

However, NPFT piping has adjusted crest and root heights. These eliminate that gap that we spoke about earlier. Thus, it eliminates any leakages that you may have experienced previously.

Variants of the NPT

You may see others refer to NPT threads by various names:

  • MPT (Male Pipe Thread)
  • NPT(M) - male (external) threads
  • FPT (Female Pipe Thread)
  • FNPT or NPT(F) - female (internal) threads
  • MIP (Male iron pipe)
  • FIP (Female iron pipe)

All of these designations refer to the same standards that we've been discussing.

What Is the National Pipe Thread vs. the British Standard Pipe?

The United States and Canada stand by the NPT (National Pipe Thread). Meanwhile, several other countries stand by the BSP (British Standard Pipe): 

  • United Kingdom
  • Europe
  • Asia
  • Australia
  • New Zealand
  • South Africa

In fact, most countries worldwide use the British Standard Pipe. But, what makes them different? And, what makes them the same?

The Similarities

Both the NTP and the BSP have the same pitch. And, they have similar peaks and valleys.

However, there is one thing that fundamentally differs these two standards from one another.

The Differences

The designs of the threads differ between these two standards. These are fundamental changes that completely alter the use of the pipe.

With the NPT, the peaks and valleys of the threads are flat. However, with the BSP, the peaks and valleys are rounded.

It's also important to point out the angle of the NPT is at 60 degrees while the angle of the BSP is at 55 degrees.

The National Pipe Thread (NPT)

The NPT, or National Pipe Thread Tapered, is the standard for the United States and Canada. These tapered threads are supposed to hold pipes and fittings together.

The American National Standard Pipe Thread developed these standards. Commonly, people refer to these as the national pipe thread standards.

NPT is one of the most technical standards for the United States. And, these standards are defined for both tapered and straight thread series. We briefly touched on this earlier.

Experts use these threads for a variety of purposes, such as rigidity and pressure sealing.

The British Standard Pipe (BSP)

The BSP, or British Standard Pipe, follows the ISO 228 standard. The thread uses Whitworth standard threads. And, it has been adopted internationally.

Among other technical standards, the BSP has spread to countries around the world. These countries stand by the technical specifications. And they use these specifications to craft pipes that can interconnect and seal pipes and fittings.

The BSP also serves as the standard for plumbing and pipe fitting around the world. In fact, it's almost adopted in every single country. And, the United States and Canada are the only countries that haven't officially adopted it.

Which Is Better: NPT Standards or BSP Standards?

Unfortunately, there isn't a clear answer to this. As engineers, we'd like to give a concrete answer. But, there isn't one.

Both sealing systems are legitimate and effective in their own ways. Neither one is better than the other.

It's important to note that both thread designs work well, even though they're different. So, there's no point in choosing one over the other. As long as they both work, they are both valid options for your projects.

Both the NPT and BSP standards have been around for over a century. And, experts have been using both threading methods for that long, too.

Both are acceptable options for your projects.

Thread Standards and Their Applications

Both NPT and BSP standards help with a variety of project all over the world. Mostly, experts use tapered threads because of the sealing abilities that we touched on earlier. But, others may use straight threads for some projects.

These piping standards exist in a variety of industries all across the world:

  • Power plants
  • Gas
  • Oil
  • Chemical
  • Manufacturing
  • Shopping

Experts also use threads of different materials to handle different jobs as well. Here are some of the most common materials that engineers use:

  • Steel
  • Brass
  • Bronze
  • Cast Iron
  • PTFE
  • PVC
  • Nylon

Like with other things, having more options is better. It can help engineers find the exact kind of pipe that they're looking for. And it makes it easier to apply pipes to different kinds of situations.

Professionals in Threading Tools

Making your way around all of these standards isn't easy. In fact, differentiating between them requires a level of expertise that most people don't have.

But that's why we're here. Our team at Wiseman has the expertise and experience that you need to figure out your next threading project.

We can help you find the right tools and get started on the right foot. We understand the differences between the National Pipe Thread standards and the British Standard Pipe. So, we can help you navigate both standards easily.

Feel free to contact us with any questions or concerns that you may have. We're happy to help.