NPSM Pipe Thread (USA)

The NPSM thread is an American pipe thread standard. It is part of the American National Standard Pipe Thread, under which many different types of pipe threads for various applications are united. The NPSM thread is suitable for general use in mechanical connections where cylindrical threads are advantageous. It is used in pipes made of iron, steel, or brass, where there is no internal pressure. The abbreviation NPSM stands for National Pipe Straight–Mechanical or American National Standard Straight Pipe Thread for Free-fitting Mechanical Joints. The NPSM thread is standardized according to ANSI Standard B 1.20.1-1983 (R1992).

The NPSM thread is a cylindrical thread with a 60° flank angle. Connections are made by combining two cylindrical threads. Thus, the NPSM thread is somewhat different from the usual pipe thread connections, where at least one of the threads used is typically tapered. The NPSM thread does not create a sealing connection.

The thread designation of the NPSM pipe thread consists of three components: a numerical value in inches, the pitch in threads per inch, and the abbreviation NPSM. A unique feature of all pipe thread types is that the numerical value in the thread designation does not stand for the external diameter. In fact, the dimensions that have been included in the thread designation refer to an outdated pipe geometry. Therefore, the external diameter of a 1″ – 11 1/2 NPSM is not exactly 1 inch, but slightly larger, at 1.315 inches or 33.401 mm.

From the NPSM thread table, you can read the correct external diameters in inches and mm. Also listed is the pitch, both in threads per inch and as a metric value. If you want to cut an NPSM thread yourself, you can use the core hole diameter indicated in the thread table. And you can access the necessary threading tools via a link!