What is NPT Thread & NPT Thread Dimensions – NPT Thread Size Chart | CNCLATHING


The threaded pipe can provide effective sealing when conveying liquid, gas, steam, and hydraulic fluid. These threads can be produced on different materials with CNC services and other techniques. One of the common standard threads is NPT, you may have heard 1/8 NPT thread and 1/2 NPT thread, what do they mean? Here we’ll explain what NPT stands for, the characteristics of NPT threads and the basics of NPT thread sizes, you can also check out the NPT thread size table.

What is NPT Thread - What Does NPT Thread Mean

NPT stands for National Pipe Thread, also known as American National Standard Pipe Thread, it is a U.S technical standard for measuring screw threads on threaded pipes and pipe fittings. NPT threads can be divided into tapered and straight thread series for different purposes. NPT is defined by ANSI/ASME standard B1.20.1.

Characteristics of NPT Threads (National Pipe Thread Tapered):

– Angle between the taper and the center axis of the pipe≈1.7899°≈ 1°47′24″

– Truncation of roots and crests are flat

– 60°thread angle

– Pitch is measured in threads per inch (TPI)


Pipe threads can be designed to various types for suiting both with or without thread sealants. For example, the National Standard Taper Pipe Thread allows them to form a seal when tightened, the larger diameter keeps compressing into a smaller diameter and finally forms a seal. 

Types of NPT Threads:

NPT: National pipe taper

NPS: National pipe straight

NPSC: National pipe straight-coupling

NPSF: National pipe straight-fuel

NPSH: National pipe straight-hose

NPSI: National pipe straight-intermediate

NPSL: National pipe straight-locknut

NPSM: National pipe straight-mechanical

NPTF: National pipe taper-fuel

NPTR: National pipe taper-railing


NPT threads can also be referred to as MPT (Male Pipe Thread) or NPT (M) for external threads, and FPT (Female Pipe Thread) or NPT (F) for internal threads. But MPT and FPT are not specified in the ANSI standard.

NPT Thread Sizes

– Commonly used NPT thread sizes including 1/8, 1/4, 3/8, 1/2, 3/4, 1, 1+1/4, 1+1/2, 2, 2+1/2, 3, 4, 5, and 6 inches, can be found on most U.S pipes and fittings. The thread sizes smaller than 1/8 inch and larger than 6 inches are occasionally used for specific purposes. 

– The pipe size in the NPT thread sizes chart does not refer to any physical dimensions, it is used as a trade size. 

– When identifying or determining a thread size, the threads-per-inch and outside diameter of the thread are necessary because there is more than one size has the same TPI. So the OD of a pipe or fitting must be measured and compared to a thread size table for identification. 

– The taper rate is 1 in 16 inch.

– Example of NPT thread designation: 1/8 – 27 NPT

– NPT and NPS threads are not interchangeable, NPT threads are tapered and NPS threads are straight, but both NPT and NPS have the same thread angle, shape and pitch.

NPT Thread Size Chart - NPT Thread Dimensions Table