What Is BSP and NPT Thread?

Threaded fittings play a crucial role in fluid systems, offering quick assembly and disassembly while allowing for easy maintenance and troubleshooting. Among the various types of threads used in hydraulics, BSP (British Standard Pipe) threads and NPT (National Pipe Thread) threads are the most common.  

NPT Thread (National Pipe Thread)  

NPT threads follow the American standard ANSI B1.20.1 and are widely used in hydraulic fittings, second only to BSP threads. They feature a 60° thread angle and are tapered (conical) rather than cylindrical, which enhances sealing performance. While NPT threads generally provide good watertightness, the use of gaskets or sealants is still recommended for optimal leak prevention.  

For identification, NPT threads may also be referred to as:  

- Male Threads: MPT, MNPT, or NPT (M)  

- Female Threads: FPT, FNPT, or NPT (F)  

Both male and female NPT threads share the same spacing, 60° angle, and flat peak-and-valley profile, ensuring compatibility across hydraulic applications.

BSP Thread (British Standard Pipe)  

BSP (British Standard Pipe) threads are widely used in Australia and Commonwealth countries, following ISO 228 and Whitworth standards. Recognized internationally, BSP threads are commonly used for connecting and sealing pipes and fittings.  

The BSP standard incorporates Whitworth threads, which were first developed in 1841 as the world’s first standardized thread system. Due to their reliability and effectiveness, BSP threads have become a globally accepted standard for pipe and fitting connections.

BSP threads are classified into two main types: BSPP (Parallel) and BSPT (Tapered), each serving different sealing mechanisms and applications.  

BSPP (British Standard Pipe Parallel)  

- Reference Standard: BS5200 – ISO 8434-6  

- Characteristics: BSPP threads are cylindrical and derived from the Whitworth thread but have different sizes and spacing. They are commonly referred to as GAS cylindrical threads.  

- Sealing Methods:  

  - A 60° concave flaring on the male fitting creates a mechanical seal.  

  - An O-ring gasket is positioned on the female fitting cone for secure sealing.  

  - A copper gasket is used when both male and female parts have a flat sealing surface.  

- Usage: Predominantly used in Europe for hydraulic and pneumatic connections.  

BSPT (British Standard Pipe Tapered)  

- Characteristics: BSPT threads are tapered and known as GAS conical threads. The seal is achieved through the deformation of the threads between the male and female parts.  

- Key Difference from NPT:  

  - BSPT has a 55° thread angle, whereas NPT has a 60° angle.  

  - While an NPT fitting may physically thread into a BSPT connection (and vice versa), they will not form a proper seal.  

- Usage: Commonly used in China and Japan but rarely seen in North America, unless used on imported equipment.

Key Differences Between BSP and NPT Threads  

The primary distinction between BSP (British Standard Pipe) and NPT (National Pipe Thread) lies in their geographical usage rather than their functionality.  

- NPT Threads are predominantly used in the USA and Canada.  

- BSP Threads are the standard in the United Kingdom, Europe, Asia, Australia, New Zealand, South Africa, and many other regions.  

Additionally, BSP and NPT threads are not interchangeable due to their differences in thread form:  

- NPT threads have a 60° thread angle and a tapered design for sealing.  

- BSP threads use a 55° thread angle and are available in both parallel (BSPP) and tapered (BSPT) forms.  

Because of these variations, attempting to connect NPT and BSP fittings may result in improper sealing and potential leaks. The NPT threads are sharp in peaks and valleys, where BSP threads are rounded. In particular, the NPT thread angle is 60 degrees compared to the BSP 55-degree angle.

Right for this last difference, it is good to choose the suitable thread in order not to cause any fluid leakages or faults under pressure.