Pipe Threads: Standards and Compatibility

Have you ever been confused about pipe thread nomenclature? Have you wondered what is the difference between NPT and PT? What about BSPT? If you have asked these questions or similar ones, you’re not alone and this paper is for you! Several different pipe thread designations are used around the world, and some are equivalent or compatible while others are not. A few of the most common types of pipe thread are listed below:

American National Standard (ASME)

NPT
NPSC
International Standard (ISO)

G
R
Rp
Rc
Historical British Standard (BS)

BSPP
BSPT
Historical Japanese Industrial Standard (JIS)

PT
PS
PF

Figure 1—Typical threaded pipe connection with thread sealant.

In the U.S., American National Standard pipe thread is the most common, but other designations are also used. This is especially true of overseas companies (or their U.S. subsidiaries), where ISO, British Standard, and JIS pipe threads are often much more prevalent. Certain pipe thread designations are equivalent and compatible, some are not equivalent but partially compatible, and others are neither equivalent nor compatible. It can be confusing to determine what is true of a particular designation. This paper aims to eliminate this confusion.