NPT VS NPTF VS NPSM

NPT VS NPTF

National Pipe Taper, commonly abbreviated as NPT, is a standard used to define the threading requirements for pipes. According to the ANSI B1.20.1 standard, pipes used for NPT should have threads that conform to specific measurements. On the other hand, National Pipe Tapered for Fuels, abbreviated as NPTF, follows the ANSI B1.20.3 standard for its threading requirements.

The main differences between NPT and NPTF threads can be found in their major and minor diameters, as well as the root and crest of their threads. The crests of NPTF threads are designed to fall within the same parameters as NPT requirements, but the crests of NPTF threads have a smaller range.

Moreover, NPTF thread roots are designed to interfere with the crest of the mating thread, creating a mechanical seal through thread form deformation during assembly. In contrast, the thread roots of NPT are designed to allow clearance with mating thread crests during assembly.

While both NPT and NPTF are designed to screw together, NPT requires a seal to be leak-proof, while NPTF does not. The gauge requirements for NPT and NPTF also differ for threads larger than ½ inch in size, making them non-interchangeable. This difference is primarily seen in the Plug Gage Major Diameter and Ring Gage Minor Diameter.

However, the most significant difference between NPT and NPTF lies in the inspection required for each. For NPT, a single plug with a step, an L1 plug for internal threads, and a single thin L1 ring for external threads are sufficient to check their size. In contrast, NPTF requires additional threads in assembly, such as L2 and L3, and the major and minor diameters must be inspected using special plug or ring gauges.

NPT VS NPSM

When it comes to pipes and connectors, there are numerous thread standards and variations. In the United States and Canada, two main types of threads are used for thermowells, namely:

NPT

American National Standard Pipe Tapered thread. This thread creates a pressure-tight seal by compressing and tightening the male and female NPT threads.

NPSM

American National Standard Pipe Straight Mechanical Joint thread. This thread creates a non-pressure tight connection that is suitable for applications that are not subject to internal pressures.

Although many applications use the same type of male and female threaded connectors, WIKA USA recommends the use of thermowells with NPSM threads when the mating thermometers have an NPT thread. Our experts have discovered that this combination is the best practice for temperature measurements.

Comparing NPT and NPSM Threads

Both NPT and NPSM connectors have the same number of threads per inch, and each thread's angle is 60 degrees. (BSPT connections, which use British Standard Pipe Threads, have a thread angle of 55 degrees.) The obvious difference between NPT and NPSM threads is that the former is tapered or slightly conical, while the latter is straight or parallel.

You may wonder why we use a tapered male fitting with a parallel female connector. Won't they bind or create awkward fits? The answer is a resounding "no." WIKA USA makes it a standard practice due to several advantages.