1. Introduction

If you ever needed to join two pipes together, either by using an union, a curve or a tee, you probabily used a thread connection. It’s the most common way to assembly a pipeline or connect pipes to equipment. It can be used in almost any type pipe material, from plastic to steel.The most used pipe threads nowadays is: NPT (American National Standard Pipe Thread), BSP (Britsh Standard Pipe), JIS (Japonese Industrial Standard) and SAE (Society of Automotive Engineers). There are other types of pipe connections that indirectly uses threads to connect the pipe, usualy through a nut, as the DIN 11851, but it will not be considered here as the thread isn’t in the pipe.

2. History

It’s quite dificult to find information about when and how threaded connections was created, the best information that I could find came from a whitepaper from CPC (Colder Products Company), which was founded in 1978 in St. Paul, Minnesota – USA. According to the document((Schmidt, C. Pipe Thread Types and Designations. Retrieved from https://www.cpcworldwide.com/)), it was usual in the nineteenth century each manufacturers create their own threaded type, which of course, caused a lot of problems. It was in 1841 that Sir Joseph Whitworth created a threading system, the Whitworth thread, based on a 55 degree thread angle with rounded roots and crests. Later it bacame known as the Britsh Standard Pipe Thread (BSP).In America, 1864, William Sellers created the National Pipe Tapered Thread (NPT) system, based in a 60 degree thread angle, comonly used by early american clockmakers. In 1906, the Association of Licensed Automobile Manufacturers (ALAM) developed what would be known today as SAE thread standard, based in the William’s thread system, but with fine thread pitch.I didn’t find any information regarding the JIS pipe thread history, but if you take in account that the JIS was founded in 1921, you could say that their thread system was the later one to be developed.

3. Threads

4. British Standard Pipe (BSP)

ISO 7-1:1994 – Dimensions, tolerances and designation
ISO 7-2:2000 – Verification by means of limit gauges
ISO 228-1:2000 – Dimensions, tolerances and designation
ISO 228-2:1987 – Verification by means of limit gauges

5. American National Standard Pipe Thread (NPT)

6. Japonese Industrial Standard – JIS

7. Society of Automotive Engineers – SAE

8. Differences Between BSP, NPT, JIS and SAE