Thread type: NPS - National Standard Straight Pipe 

Cylindrical standard gas thread for female thread

The thread that we present to you in the NPS thread table belongs to the family of American pipe threads. Pipe threads can generally be distinguished by their shape, which can be conical or cylindrical. Another important criterion is whether the thread is sealing or non-sealing. NPS stands for National Pipe Straight. According to the NPS thread table, this describes the thread as a parallel pipe thread, i.e. a cylindrical design. The values in the NPS thread table correspond to the specifications defined by the American National Standards Institute (ANSI) in the ANSI B 1.20.1 standard. It must be distinguished from the conical pipe thread NPT.Although both threads can generally be screwed together, they do not seal properly.

The NPS thread has a flank angle of 60°. As you can see from the NPS thread table, it is an imperial thread. As with most inch pipe thread types, it is important to pay attention to a special feature regarding the inch dimension. If the NPS thread table refers to an outer diameter of 1", then this does not correspond to 25.4 mm, as would be assumed. Instead, a 1" pipe has an outer diameter of 33.25 mm. This is because the term 1" historically referred to the internal diameter of pipes, which has changed considerably due to technical innovations. However, the designation 1" was retained despite the lack of reference - as in the NPS thread table.

The table for the NPS thread covers thread sizes from 1/16" to 2", whereby the abbreviation NPS is still placed in front of the inch designation for the thread designation. The actual outside diameter, which differs from the thread designation as described above, can also be found in the NPS thread table, as can the number of threads per inch. We have also listed the conversion of the outside diameter into mm in our NPS thread table if you prefer to work with metric data. The pitch is also given in mm accordingly.

 Major Diameter InchMajor Diameter mmTPIPitch P
NPS 1/16"0,1303,2927,00,941
NPS 1/8"0,2596,5827,00,941
NPS 1/4"0,51813,1618,01,411
NPS 3/8"0,65616,6618,01,411
NPS 1/2"0,82520,9514,01,814
NPS 3/4"1,04126,4414,01,814
NPS 1"1,30933,2511,52,209
NPS 1.1/4"1,65041,9111,52,209
NPS 1.1/2"1,88247,8011,52,209
NPS 2"2,34759,6111,52,209

Please note:
The Major Diameter of 1" Inch Pipe Thread is 33,25 mm or 1,309 Inches (not 25,4 mm)!
Historically it had it's origin from the manufacture of steel pipes in the beginning of the 20th century. In that time the normal 1" Inch pipes with the internal diameter of 1" Inch had a outside diameter of 1.309 Inches (about 33 mm).

Cross section of an NPS thread