Thread Types

BSP

BSP thread form stands for British Standard Pipe and is common in Australia and the commonwealth countries. It is based on trade size rather than actual diameter which can lead to some confusion when measuring ports.

There are two types of BSP threads;
- Parallel (BSPP) - also known as G or Rp
- Tapered (BSPT) - also known as R or Rc

Both threads have the same pitch, angle (55 degrees) and shape (rounded peaks and valleys).

The below table gives the major and minor diameter for each BSP Trade Thread Size.

NPT

NPT stands for National Pipe Thread and is an American standard thread. It may also be referred to as MPT, MNPT or NPT (M) for male external threads and FPT, FNPT or NPT(F) for female internal threads. A thread sealant must always be used to achieve a leak-free seal (except for NPTF). It is also based on Trade Size rather than the actual diameter (similar to BSP in this regard).

Both threads have the same pitch, angle (60 degrees) and shape (flat peaks and valleys).

The below table gives the Threads Per Inch, Pitch and Major Diameter for NPT Threads.

BSP vs NPT

NPT threads are common in the United States and a few other countries, BSP threads are widely used in many other countries.

BSPT -British Standard Pipe Taper
BSPP -British Standard Pipe Parallel
NPT -National Pipe Taper
NPS -National Pipe Straight

While the actual specified outside diameters of American National Pipe differ slightly from those of British Standard Pipe, either thread may reliably be cut onto a pipe of its respective trade size. BSPT equivalent is NPT and BSPP's equivalent is NPS.

Never swap threads if it is a high-pressure application.

NPT/NPS and BSP threads are not compatible due to the differences in their thread forms, and not just the fact that most sizes have a different pitch. NPT/NPS threads have a 60° angle and have flattened peaks and valleys (Sellers thread form) whereas BSP threads have a 55° angle and have rounded peaks and valleys (Whitworth thread form).

NPT and BSP thread pitches (threads per inch) are listed below. To determine pitch, use a thread gauge or count the number of threads that fall into a 1" span.