If you’ve ever worked with piping systems, you’ve probably come across NPT threads—but what exactly do they mean? NPT (National Pipe Taper) threads are one of the most widely used thread types for sealing pipes and fittings in industrial, plumbing, and manufacturing applications. Designed to create a tight, leak-resistant seal, NPT pipe threads rely on their tapered design rather than a gasket to prevent leaks.
Understanding NPT thread specifications, sizes, and how they compare to other thread types like NPTF (National Pipe Taper Fuel) is essential for choosing the right fitting for the job. From 1/8 NPT drill size to larger NPT pipe thread dimensions, using the correct size and following an NPT thread chart ensures a proper fit and a secure connection.
What is NPT?
NPT, or National Pipe Taper, is a standardized thread type used for sealing pipes and fittings in a wide range of industries, including plumbing, hydraulics, and manufacturing. Unlike straight threads, which require gaskets or O-rings to prevent leaks, NPT threads rely on their tapered design to create a tight seal. As the male and female NPT fittings are screwed together, the threads compress, forming a secure, leak-resistant connection.
The taper is a key feature of NPT pipe threads, with the diameter decreasing at a rate of 1/16 inch per inch of length. This gradual narrowing ensures a snug fit that improves with tightening. However, to fully prevent leaks, many professionals use thread sealant or PTFE tape when assembling NPT fittings.
Chart Example
Below is a sample of NPT thread fitting chart:
| Nominal Size | Threads Per Inch | Outside Diameter (in) | Pitch (in) | Taper (in/ft) | Thread Length (in) | Effective Thread Length (in) | Hand-Tight Engagement (in) |
| 1/16 | 27 | 0.3125 | 0.03704 | 3/4 | 0.2611 | 0.1615 | 0.0644 |
| 1 | 11.5 | 1.315 | 0.08696 | 3/4 | 0.6828 | 0.402 | 0.2006 |
| 2 | 11.5 | 2.375 | 0.08696 | 3/4 | 0.7565 | 0.4752 | 0.2219 |
| 3 | 8 | 3.5 | 0.125 | 3/4 | 1.2 | 0.6083 | 0.2542 |
| 4 | 8 | 4.5 | 0.125 | 3/4 | 1.3 | 0.6542 | 0.2604 |
| 5 | 8 | 5.563 | 0.125 | 3/4 | 1.4063 | 0.7042 | 0.2667 |
Advantages of NPT Threads
The main advantage of NPT pipe threads is their ability to create a leak-resistant connection without the need for additional sealing components. This makes them ideal for high-pressure applications where a secure fit is essential. However, to ensure a proper seal, thread sealant (such as PTFE tape or pipe dope) is often used when assembling NPT fittings.
NPT vs. NPTF
A common point of confusion is the difference between NPT vs. NPTF (National Pipe Taper Fuel). While both thread types have the same basic dimensions, NPTF threads are designed to create a dry seal without the need for thread sealant. In contrast, standard NPT threads typically require sealant to prevent leaks. This distinction is especially important in applications where avoiding fluid contamination is critical.
Standardization and Usage
NPT thread specifications are governed by ANSI/ASME B1.20.1, which defines the thread dimensions, taper angle (1° 47′), and number of threads per inch (TPI) for different NPT sizes. These standards ensure compatibility across various manufacturers and industries, making NPT fittings widely used in plumbing, hydraulics, and compressed air systems.
Parting Thoughts
MISUMI USA carries a large array of products with NPT threads, including the following:
Thread Pipe Fittings & Flanges – NPT (Male)
Thread Pipe Fittings & Flanges – NPT (Female)
Fittings for Steel & Copper Pipes-NPT
For questions on products related to NPT thread fittings, or any other product questions please connect with our product experts and engineers. And, for more articles on things related to industrial manufacturing and engineering check out more of our blog.
Disclaimer
The content on this webpage is for informational purposes only. MISUMI makes no guarantees, expressed or implied, regarding the accuracy, completeness, or validity of the information. Performance parameters, tolerances, designs, materials, or processes should not be assumed to reflect third-party suppliers’ or manufacturers’ deliverables within MISUMI’s network. Buyers are responsible for specifying their part requirements