National Pipe Thread | NPT Thread Chart

  National Standard Pipe Thread | NPT Thread

American National Standard Pipe Thread standards, often called national pipe thread standards for short NPT, are U.S. national technical standards for screw threads used on threaded pipes and pipe fittings.

They include both tapered and straight thread series for various purposes including rigidity, pressure-tight sealing, or both. The various types are each named with a symbol and a full name; examples of the symbols include NPT, NPS, NPTF, NPSC, and others.

Outside the United States, some US pipe threads are found, as well as many British Standard Pipe threads and ISO 7-1, 7-2, 228-1, and 228-2 threads.

NPT is NATIONAL PIPE TAPER (AMERICAN) – Thread form per ANSI/ASME B1.20.1

NPS is NATIONAL PIPE STRAIGHT (PARALLEL) – Thread form per ANSI/ASME B1.20.1

NPTF is NATIONAL PIPE TAPER FOR FUEL – Thread form per SAE J476

NPSM is NATIONAL PIPE STRAIGHT MECHANICAL – Thread form per ANSI/ASME B1.20.1

  National Standard Pipe Taper Thread | NPT Thread

NPT thread full form is National pipe taper thread. It's also known as American National Standard Taper Pipe Thread. Tapered for sealing, often without any thread sealant, for connections in nearly every type of service

  National Standard Pipe Straight Thread | NPS Thread

NPS thread full form is National pipe straight thread. It's also known as American National Standard Straight Pipe Thread. For rigidity, for sealable only with sealant, sometimes male straight enclosed by female tapered for low-pressure sealing.

  National Standard Pipe Thread (NPT) Use

Threaded pipes can provide an effective seal for pipes transporting liquids, gases, steam, and hydraulic fluid. These threads are now used in materials other than steel and brass, including PTFE, PVC, nylon, bronze, and cast iron.

The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings or compression fittings in which the threads merely hold the pieces together and do not provide the seal. The various types of pipe threads are designed for use both with or without thread sealants, as particular applications demand.

As the thread body is tapered, a larger diameter keeps compressing into a smaller diameter and finally forms a seal (no clearance remains between the crests and roots of the threads because of the taper). This means that NPT fittings should be burr-free and lubricated using a lubricant like lubricating paste or thread seal tape. The use of tape also helps to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.

Commonly used sizes are ​1/8, ​1/4, ​3/8, ​1/2, ​3/4, 1, ​1-1/4, ​1-1/2 and 2", appearing on pipes and fittings by most U.S. suppliers. Sizes smaller than ​1/8 inch are occasionally used for compressed air, while sizes larger than 2 inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes.

  Thread Count (TPI)

TPI stands for Threads Per Inch, Means the total number of threads per inch measured along the length of a fastener. TPI is used only with American fasteners. Metric Fasteners use a thread Pitch. In general, smaller fasteners have finer threads, so the thread count is higher.

  Thread Pitch

Metric fasteners are specified with a thread pitch instead of a thread count. The thread pitch is the distance between threads expressed in millimeters. In general, smaller fasteners have finer thread so they have lower thread pitch.

  NPT Thread Charts

NPT Thread Chart

  National Standard Pipe Thread Chart | NPT Taper Thread Chart

Size & Pitch External Thread OD Internal Thread ID
inch TPI mm inch mm inch
1/8 27 9.9  0.39 8.4  0.33
1/4 18 13.2  0.52  11.2 0.44
3/8 18  16.6  0.65 14.7 0.58
1/2 14 20.6 0.81 17.8 0.7
3/4 14 26.0 1.02 23.4 0.92
1 11.5 32.5 1.28 29.5 1.16
1-1/4 11.5 41.2 1.62 38.1 1.5
1-1/2 11.5 47.3 1.86 43.9 1.73
2 11.5 59.3 2.33 56.4 2.22
2-1/2 8 71.5 2.82 69.1 2.72
3 8 87.3 3.44 84.8 3.34

  National Standard Pipe Thread Chart | NPSM Thread Chart

Size & Pitch External Thread OD Internal Thread ID
inch TPI Max Min Max Min
1/8 27 0.397 0.390 0.358 0.364
1/4 18 0.526 0.517 0.468 0.481
3/8 18 0.662 0.653 0.603 0.612
1/2 14 0.823 0.813 0.747 0.759
3/4 14 1.034 1.024 0.958 0.970
1 11.5 1.293 1.281 1.201 1.211
1-1/4 11.5 1.638 1.626 1.546 1.555
1-1/2 11.5 1.877 1.865 1.785 1.794
2 11.5 2.351 2.339 2.259 2.268
2-1/2 8 2.841 2.826 2.708 2.727
3 8 3.467 3.452 3.334 3.353
3-1/2 8 3.968 3.953 3.835 3.848
4 8 4.466 4.451 4.333 4.346

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