DonyRony LOGO

What is NPT in Brass Fittings? Understanding Brass NPT

1:8 NPT brass fitting

NPT brass fittings are standard in many applications, from home to industrial and even automotive systems. But what does the use of NPT in brass fittings mean? This post aims to help you understand what using brass fittings bearing the NPT thread means for your project or application.

Are Brass Fittings NPT?

Not all brass fittings are NPT. Only those that bear the NPT thread are. When not NPT, brass fittings are other thread types such as NPS (national pipe straight) or NPTF (National pipe thread fuel).

NPT fittings offer several advantages, which, among other things, explain their widespread use in industrial and plumbing applications.

  • NPT threaded fittings make secure connections that will not leak.
  • You can safely use them in many different applications, including water, air, gas, and oil
  • They come in many different configurations such as elbows, tees, and straights
  • The different NPT thread sizes that you can use in a broad range of applications, from residential plumbing to automotive systems

The NPT thread is available in various fitting materials, from brass to stainless steel. So, what does it mean when brass fittings are NPT? Let’s see.

Brass fitting NPT thread sizes
Brass fitting NPT thread sizes
Resource: https://forum.iktva.sa

What is NPT in Brass Fittings?

When used in brass fittings, NPT denotes the type of thread used. The threaded section of a brass NPT type of fitting is a tapered design. That means the thread size decreases along the fitting length, making it assume a cone shape.

NPT in full is National Pipe Thread. It means a US standard for the thread of fitting and other connections. The ASME B1.20.3 standard defines the type of threading called NPT in brass fittings.

You might also come across the NPTF standard for fittings. While these two feature similar configurations, a few differences distinguish each from the other.

NPTF is National Pipe Thread Fuel, defined by ASME B1.20.1. It commonly designates the thread design for high-pressure, high-temperature connections.

National pipe thread brass fittings sizes illustrated
National pipe thread brass fittings sizes illustrated
Resource: https://theamcforum.com

Brass NPT Fitting Specifications

Brass NPT fittings are available in various sizes. They also have a pressure range within which you must use them. Most importantly, you can only tighten NPT fittings up to a specific torque level, or the thread may get damaged. Here’s more about these recommendations.

Brass NPT Fittings Sizes

Brass NPT fitting manufacturers make the product in various sizes. The smallest fitting of this type can be as small as ⅛ inches and the largest 2 inches. Standard NPT brass fitting sizes include those listed below.

  • 1/4 inches,
  • 1/8 inches
  • 3/8 inches
  • 1/2 inches
  • 3/4 inches

Note that the above-listed sizes are nominal and do not represent the actual fitting sizes. For exact dimensions, you need the help of a chart with nominal values and their conversion to actual sizes.

Brass NPT Fittings Pressure Rating

You can only use brass NPT fittings at specified pressure levels. The pressure range typically depends on the type of fitting and tube, their materials, and other factors such as size and operating heat levels.

Generally, you can use NPT fittings made from brass in up to 3000 psi. Again, the actual pressure will depend on the mentioned factors and varies across the different types of the device.

NPT Brass Fitting Torque

The Brass fitting NPT thread requires appropriate tightening. Too much torque, and you risk galling the thread. Owing to their tapered design, they make tight connections by interference and should not bottom during tightening.

Brass materials are also relatively soft and malleable. Anyone using brass fitting that bears the NPT thread (or any other thread) should, therefore, not tighten them too much, especially when using a tool.

A 14 inch NPT tee brass fitting
A 1/4 inch NPT tee brass fitting
Resource: https://www.researchgate.net

Can You Use Brass NPT on Steel?

You could. However, experts do not recommend using brass NPT fittings on steel pipes. Brass is the softer material in this combination. You risk getting it damaged and the thread galling when tightened.

Obtaining a proper seal when using brass fittings on steel pipes would also be challenging. Such connections would likely leak, especially if the media is a non-viscous fluid or air.

Depending on the type of brass and steel used and the application environment, combining the two dissimilar metals could also cause galvanic corrosion. Read more about galvanic corrosion here.

How to tighten brass NPT fitting
How to tighten brass NPT fitting
Resource: https://www.plumbermag.com

How to Tighten Brass NPT Fittings

The use of NPT in brass fittings means a secure mechanical connection. However, the tapered construction makes them pliable to thread damage. So, how do you safely tighten a brass fitting using the NPT thread? Always follow these rules:

  • Always start by tightening the fitting with your fingers.
  • That often means 2 to 4 turns, depending on your type of fitting and size.
  • Once the connection is finger-tight, you can use a wrench.
  • When tightening with a wrench, the general rule is to ensure 1.5 to 2 turns.
  • Avoid cross-threading the fitting by not forcing it to tighten. In the event of resistance, remove it and try again.
  • If using sealant tape, do not do not apply too much or even too little. About 1 or 2 wraps are enough to ensure a secure connection.
  • Before installing and tightening a brass NPT fitting, ensure the thread is in good condition. If necessary, clean it first.

Conclusion

NPT in brass fittings means brass fittings that a manufacturer builds to the NPT standard. These fittings are popular in many applications, given their advantages, such as exceptional sealing, secure connections, and more.

But while the NPT thread makes them superior in many ways, these fittings must be used carefully. Among other things, always avoid over-tightening them. Use them with suitable pipes to protect the thread and ensure secure connections.

Contact US

Contact Us