NPT and BSP Threads

RELAB has been manufacturing various spray nozzles and fittings with different thread standards: Metric and Imperial. They are the most commonly used in our products.

What are the NPT threads?

NPT threads are the abbreviation for National Pipe Thread Tapered, which are the U.S. standard for tapered threads used to join pipes and fittings. Also, the NPT thread angles are 55°.

The NPT thread is widely used in the United States, Canada and Mexico. Within the American National Pipe standard, there are unique sub-categories including National Pipe Tapered (NPT) and National Pipe Straight (NPS).

* NPT -National Pipe Taper
* NPS -National Pipe Straight

Visual Difference between NPT and NPS:

What are the BSP threads?

BSP threads are the abbreviation for British Standard Pipe, are among a number of technical standards for screw threads that have been adopted internationally for interconnecting and sealing pipes and fittings. Also, the BSP thread angles are 60°.

BSP threads are widely used in many other countries, are designated by trade size, rather than actual diameter.

There are two popular thread forms: British Standard Pipe Parallel (BSPP) and British Standard Pipe Tapered (BSPT). Identification is made by measuring the outside diameter of the thread and the number of threads per inch (25.4 mm).

* BSPT: British Standard Pipe Taper -also known as R threads
* BSPP: British Standard Pipe Parallel -also known as G threads

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 and BSPP threads are analogous to NPT and NPS threads, respectively.

What is the difference between NPT/NPS and BSP threads?

1. Different Thread angle and form

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

2. Different thread pitches

NPT and BSP thread pitches (threads per inch, TPI) are listed below. To determine pitch, use a thread gauge or count the number of threads that fall into a 1" span. Note that, strictly speaking, when we use threads per inch, we are actually specifying the inverse of the pitch, pitch being in units of [length] / [peak to peak]. Metric threads are usually specified in actual pitch, e.g., 1.5mm, 2.0mm, etc. This is the actual length of each thread, peak to peak. Although the term "pitch" is universally used, albeit loosely, to describe threads per inch, the actual pitch of a 1/4” BSP fitting is really 1/19 inch, or 0.0526 inches.

So the NPT and BSPT threads are the same type as tapered pipe threads, and the NPS and BSPP threads are the same type as parallel pipe threads.