NPSF Pipe Thread (USA)

The NPSF thread is a pipe thread from the USA that belongs to the American National Standard Pipe Thread. This collection of thread standards includes a large number of pipe threads for both general and very specialized purposes. NPSF stands for National pipe straight–fuel and oil or Dryseal American Standard Fuel Internal Straight Pipe Thread. It is the cylindrical counterpart to the tapered NPTF thread. The name addition "straight" indicates the cylindrical shape, while "fuel and oil" points to the main application area in the field of fuels. The NPSF thread is standardized according to ANSI B 1.20.3.

The NPSF thread is a cylindrical pipe thread with a 60° flank angle. There is only an NPSF internal thread, which is combined with an NPTF external thread. The union between the cylindrical NPSF thread and the tapered NPTF thread creates a dry-seal connection even without the use of a sealing compound.

The NPSF thread is identified by a numerical value, the pitch in threads per inch, and the abbreviation NPSF. Unlike usual, this numerical value does not reflect the external diameter of the thread – a characteristic common to all pipe threads. The reason lies in the long history of pipe thread standards, which were developed at a time when the pipes used for these threads had different dimensions. Therefore, a thread marked 1″ – 11 1/2 NPSF actually has an external diameter of 1.288 inches or 32.718 mm.

Due to this peculiarity, it is especially important to carefully examine the NPSF thread table to determine the correct values for the respective external diameter. With only seven entries, the thread table for the NPSF thread is quite concise. The table below also provides the pitch in threads per inch and in mm. Likewise indicated is the core hole diameter at the thin pipe end in mm. For tools for the NPSF thread, simply click on the corresponding link.