National Pipe Thread Taper (NPT) is a U.S. standard for tapered threads used on threaded pipe and fittings. In contrast to the straight threads found on bolts, the tapered  are pulled tight, thus creating a fluid seal.

National Pipe Taper Fuel (NPTF), also known as Dry seal American National Standard Taper Pipe Thread, defined by ASME B1.20.3, is designed to provide a more leak-tight seal without the use of Teflon tape or other compounds. NPTF threads are the same basic shape. Instead, the peak and root heights are adjusted to fit interference, eliminating thread leakage paths.

Feature
• The angle between the taper and the center axis of the pipe is 1o 47′ 24” (1.7899o).
• Cutting the roots and shoots flat
• Thread angle 60 degrees
• Pitch is measured in threads per inch.

Pipe size does not refer to any physical dimensions. The outside diameter of the pipe or fitting must be measured and compared with a table to determine the size. 3/4″ NPT pipe threads have an outside diameter – OD – 1.050 inches.

Each thread size has a designated number of threads per inch – TPI or pitch. 3/4″ NPT pipe threads have 14 threads per inch. Both TPI and OD of the thread are required to positively identify the thread size, as TPI is the same. more than one size

NPT are not interchangeable with NPS – National Pipe Straight.

NPT may look similar to ISO 7/1 threads. However, ISO and NPT threads should not be mixed. ISO threads have a taper angle of 55 degrees, compared to 60 degrees for NPT. NPT root and peak configurations also differ from those for ISO. Thread pitch is usually measured in millimeters. (May be expressed in inches) Different spacing.