PT threads and RC threads are often compared, are they actually interchangeable? What are the differences
between them? In this article, we will discuss the characteristics of these two types of threads, application scenarios,
and the differences between them to help you better understand and choose the right thread type.
Ⅰ、Definitions and standards for PT and RC threads
1. PT thread, refers to the pipe thread, is 55 ° sealing cone pipe thread, by the British Standard Whitworth pipe
thread，referred to as BSPT evolved. Our national standard GB/T7306-2000 “55 ° sealing pipe thread” on its
provisions. PT thread taper for 1:16, that is, along the direction of the thread axis every 16mm forward, the thread
diameter will increase by 1mm.
2. RC thread, refers to the cone internal thread, is the United States standard NPT thread variant, the same taper
of 1:16. The taper is also 1:16. Unlike PT threads, RC threads are usually used to connect fittings with cylindrical
internal threads.
3. Although PT threads and RC threads have the same taper, they have different parameters such as thread type
and pitch, so they cannot be used directly interchangeably. If they are forcibly interchanged, it may lead to poor
sealing of the connection or even damage the threads.
Ⅱ、Application scenarios for PT and RC threads
1. PT thread is mainly used for water pipe, gas pipe, steam pipe and other fluid transportation pipe connection,
as well as some need to seal the connection occasions.
2. RC threads are mainly used for connecting fittings whose internal threads are cylindrical, such as some valves,
joints and so on.
Ⅲ、Main differences between PT and RC threads
1. Different standard: PT thread is the national standard GB/T7306-2000, and RC thread is a reference to the
U.S. standard NPT thread variant.
2. Tooth type and pitch: PT threads and RC threads have differences in tooth type and pitch, which is the main
reason why they are not interchangeable.
3. Application scenario: PT thread is mainly used for connecting pipes, while RC thread is mainly used for
connecting fittings whose internal thread is cylindrical.
Ⅳ、How to choose the right type of thread
1. Choose according to the type of connector: if the connection is needed for two pipes, PT thread should be chosen;
if the connection is needed for pipes and fittings with cylindrical inner threads, RC thread or other more suitable
thread types should be chosen.
2. According to the use of environmental selection: different thread types are suitable for different pressure
and temperature environments, the selection of these factors need to be considered.
3. Check the relevant standards: when selecting the thread type, it is best to check the relevant national standards
or industry standards to ensure that the selected thread type meets the requirements.
V、Sealing of PT threads with RC threads
1. Both PT threads and RC threads rely on taper for sealing, so a certain amount of torque needs to be applied
when connecting to ensure that the threads are fully engaged.
2. In order to improve sealing, sealing tape or sealant is usually used on the threaded connection.
3. Note: PT threads and RC threads cannot be used interchangeably even if sealing tape or sealant is used.
