NPT Thread Pitch Chart

What is an NPT Thread?

NPT stands for National Pipe Taper, a widely used American pipe thread standard defined by ASME B1.20.1. NPT threads feature a distinctive 60° thread profile with flattened peaks and valleys, designed for durability and consistent performance.

A key characteristic of NPT threads is their tapered design—the thread diameter increases along the length of the thread. This taper allows male and female threads to tighten together and create a pressure-tight seal, typically with the use of thread sealant. This makes NPT threads ideal for applications where leak-free connections are critical.

Although NPT is an American standard, NPT threads are commonly used throughout North America and are also found in Australian industrial equipment, imported machinery, hydraulics and pneumatic systems. Understanding NPT specifications is essential for anyone working with these systems.

NPT vs BSPT Threads

While NPT and BSPT threads may look similar at first glance, they are fundamentally different and not interchangeable. Here's how they compare:

NPT (National Pipe Taper)

• 60° thread angle
• American pipe thread standard
• Measured using threads per inch (TPI)
• Commonly used in US manufactured equipment and components

BSPT (British Standard Pipe Taper)

• 55° Whitworth thread angle
• British pipe thread standard
• Commonly used internationally, including Australia

The differences in thread angle, pitch and dimensions mean that NPT and BSPT threads cannot be safely mixed. Using the wrong thread type can result in poor sealing, leaks and potential equipment failure. Always verify the correct thread standard for your application.

How to Read the NPT Thread Chart

The NPT thread chart above provides essential specifications for common National Pipe Taper thread sizes. Here's what each column represents:

• Diameter – The nominal pipe size (e.g., 1/8", 1/4", 1/2")
• TPI – Threads Per Inch, indicating how many threads fit within one inch of length
• Drill Size (mm) – The recommended tap drill size in millimetres for creating the threaded hole

It's important to note that NPT thread sizes refer to nominal pipe sizes, and the actual outside diameter of the thread will be larger than the stated size. For example, a 1/2" NPT thread has an actual outside diameter of approximately 0.840 inches. Always refer to the complete NPT thread dimensions when selecting tools or components.

Common Applications

NPT threads are found in a wide range of industrial and commercial applications where reliable, pressure-tight connections are essential:

• Hydraulic systems and components
• Pneumatic equipment and air lines
• Industrial machinery and equipment
• Pumps, valves and flow control devices
• Compressed air systems
• Manufacturing equipment
• Automotive applications
• Fluid handling systems

Understanding NPT thread specifications ensures you select the correct taps, dies and drill bits for your specific application, resulting in secure connections and optimal performance.

Frequently Asked Questions

What does NPT stand for?

NPT stands for National Pipe Taper, an American standard for tapered pipe threads defined by ASME B1.20.1.

Are NPT and BSPT threads the same?

No. NPT uses a 60° thread angle and is an American standard, while BSPT uses a 55° Whitworth thread angle and is a British standard. They are not interchangeable.

What is the difference between NPT and NPTF?

NPTF (National Pipe Taper Fuel) is a variation of NPT with tighter tolerances, designed specifically for fuel and other critical applications where maximum sealing is required.

Do NPT threads require thread sealant?

Yes, NPT threads typically require thread sealant (such as PTFE tape or pipe dope) to create a reliable, leak-free seal. The tapered design helps create a mechanical seal, but sealant ensures optimal performance.

Are NPT threads used in Australia?

While BSPT is the primary standard in Australia, NPT threads are commonly found in imported machinery, hydraulic systems and equipment manufactured in North America.

How do I identify an NPT thread size?

NPT thread sizes are typically marked on the component or documented in equipment specifications. You can also measure the outside diameter and count the threads per inch to identify the size using a pipe thread reference chart.