The two most popular thread styles in the world are British Standard Pipe (BSP) and National Pipe Taper (NPT). They are the international standard for joining fittings and pipes. However, the difference between these thread styles is something to note.
BSP Thread
BSP is the abbreviation of British Standard Pipe. Threads, as defined in the ISO 228 standard, use Whitworth standard threads and are one of many technical standards that have been adopted internationally for the threads of interconnecting and sealing pipes and fittings. Almost worldwide, it has been adopted as the standard for pipes and pipe fittings.
Straight thread: cooperate with the matching straight thread and rely on the end face of the sealing ring to seal.
Oblique thread: Mates with the same straight thread or oblique thread, relying on thread coating to seal.
NPT Tthread
NPT stands for National Pipe Thread, which is an American standard thread. Male threads may also be called MPT, MNPT or NPT(M) and female threads may be called FPT, FNPT or NPT(F). Thread sealants must always be used to achieve a leak-tight seal (except NPTF). It is also based on trade size rather than actual diameter (similar to BSP in this respect).
Mates with threads of the same standard and relies on thread coating to seal
Difference between BSP and NPT threads
BSP and NPT threads are more about where than what, which is an important distinction. NPT is prevalent in the US and Canada, while BSP is the main standard in the UK, Europe, Asia, Australia, New Zealand, South Africa and many other countries.
Due to the different thread forms, NPT and BSP threads are not interchangeable. NPT threads point to the peaks and troughs, BSP is round. Most notably, NPT has a 60-degree thread angle, while BSP has a 55-degree angle.
Despite what has been tried, problems always arise when attempting to connect male NPT threads to female BSPP threads. Different pitches will allow the threads to be misaligned which can lead to fluid leakage or even catastrophic failure under pressure
Standardization
With the onset of the Industrial Revolution in the early 19th century, the need for thread standardization began in earnest. Standardization is needed to facilitate compatibility between different manufacturers and users.
The American standard for tapered threads was established in 1864. Subsequently, as director of the Franklin Institute, he proposed a new set of standards for nuts, bolts, and screws to replace the less standardized threading practices in the United States. His thread design gained wide acceptance largely because of the flat peaks and valleys, and the 60 degree angle was easier for the average machinist to fabricate and produce.
As early as more than two decades ago, in 1841, Joseph Whitworth proposed his thread design, which was quickly adopted by many British railway companies and became the national standard of the United Kingdom, known as the British British Standard Whitworth.
Although the standard was still used frequently in the United States and Canada until the 1860s, it was not universally accepted and often competed with many other standards used by many companies. When his standards were used for work done under government contracts, the Sellers thread eventually won in the United States and then became the standard for influential railroad industry companies. Many companies soon followed suit and it was adopted as a national standard in the United States
Application
NPT and BSP tapered threads are used because, unlike straight threads, tapered threads can be tensioned to create a fluid or airtight seal. Straight thread applications are designed to simply hold components together, while tapered threads compress and seal the joint when torque is applied.
The application of tapered threaded pipe provides an effective seal for pipes conveying liquid, gas, steam and hydraulic oil. They are used in a wide range of industries - power plants, gas and oil, chemicals, manufacturing and shipping. For example, many pressure systems on ships use BSPs, while many applications in the oil and gas industry use NPT fittings. NPT and BSP threads have been widely used in various materials. In addition to steel and brass, threads are also used in bronze, cast iron, and plastics such as PTFE, PVC, and nylon.
These two sealing systems are not inherently better than each other these days. Despite having two different designs, each thread works efficiently.
