Pressure systems in the process industry use different sealing methods depending on geographical region, system size, and environmental conditions. Regional standards and industry preferences play a key role in determining which type of fitting and seal is used. For instance, many marine and shipboard pressure systems rely on BSPP adapters, while applications in the oil and gas sector ，hydraulic and plumb system often utilize NPT fittings. Below is a concise overview of each thread type, highlighting their ideal applications and the regions where they are most commonly used.
So this article our yuhuan hongqian machinery co.,ltd make up all related detal for the bspt vs npt , hope could explain and introduce clear in this blog .
What is NPT thread ?
NPT (National Pipe Taper) thread mean is a U.S. standard for tapered pipe threads used for sealing pipes and fittings. Key features of NPT threads are:
-
Thread Angle: The threads have a 60° angle, which defines the shape of the thread profile.
-
Taper: The threads are tapered along the axis with a standard taper of 1:16, meaning the diameter decreases by 1 unit for every 16 units of length.
-
Thread Outer Diameter: The major (outer) diameter is flat, used for measuring and mating with the corresponding internal thread.
-
Sealing Method: The taper creates mechanical grip and a leak-proof seal, which can be further enhanced with thread sealant.
NPT threads come in male (external) and female (internal) types, with the seal achieved by the taper fit when tightened.
| Nominal Size (NPS) | Threads per Inch (TPI) | Major Diameter (OD) | Pitch Diameter (PD) | Minor Diameter (ID) | Taper | Pitch (P) |
|---|---|---|---|---|---|---|
| 1/8" | 27 | 10.242 mm | 9.489 mm | 8.737 mm | 1:16 | 0.941 mm |
| 1/4" | 18 | 13.616 mm | 12.487 mm | 11.358 mm | 1:16 | 1.411 mm |
| 3/8" | 18 | 17.055 mm | 15.926 mm | 14.797 mm | 1:16 | 1.411 mm |
| 1/2" | 14 | 21.223 mm | 19.772 mm | 18.321 mm | 1:16 | 1.814 mm |
| 3/4" | 14 | 26.569 mm | 25.117 mm | 23.666 mm | 1:16 | 1.814 mm |
| 1" | 11.5 | 33.227 mm | 31.461 mm | 29.694 mm | 1:16 | 2.209 mm |
| 1-1/4" | 11.5 | 41.984 mm | 40.218 mm | 38.451 mm | 1:16 | 2.209 mm |
| 2" | 11.5 | 60.091 mm | 58.325 mm | 56.558 mm | 1:16 | 2.209 mm |
| 2-1/2" | 8 | 72.699 mm | 70.159 mm | 67.619 mm | 1:16 | 3.175 mm |
| 3" | 8 | 88.608 mm | 86.068 mm | 83.528 mm | 1:16 | 3.175 mm |
What is BSPT thread ?
BSPT (British Standard Pipe Taper) is a type of tapered pipe thread commonly used in Europe and Asia for sealing and connecting pipes. It features a 55° thread angle and a tapered design that allows the threads to tighten and create a mechanical seal, often enhanced with thread sealant. BSPT threads are widely used in plumbing, hydraulic systems, and industrial piping。
BSPT thread chart
| Nominal Size (NPS) | Threads per Inch (TPI) | Major Diameter (OD, mm) | Pitch Diameter (PD, mm) | Minor Diameter (ID, mm) | Taper | Pitch (P, mm) |
|---|---|---|---|---|---|---|
| 3/8" | 19 | 16.662 | 15.806 | 14.95 | 1:16 | 1.337 |
| 1/2" | 14 | 20.955 | 19.793 | 18.631 | 1:16 | 1.814 |
| 3/4" | 14 | 26.441 | 25.279 | 24.117 | 1:16 | 1.814 |
| 1" | 11 | 33.249 | 31.770 | 30.291 | 1:16 | 2.309 |
| 1-1/4" | 11 | 41.910 | 40.431 | 38.952 | 1:16 | 2.309 |
| 1-1/2" | 11 | 47.803 | 46.324 | 44.845 | 1:16 | 2.309 |
| 2" | 11 | 59.614 | 58.125 | 56.656 | 1:16 | 2.309 |
| 2-1/2" | 11 | 75.184 | 73.705 | 72.226 | 1:16 | 2.309 |
| 3" | 11 | 87.884 | 86.405 | 84.926 | 1:16 | 2.309 |
| 4" | 11 | 113.030 | 111.551 | 110.072 | 1:16 | 2.309 |
| 5" | 11 | 138.430 | 136.951 | 135.472 | 1:16 | 2.309 |
| 6" | 11 | 163.830 | 162.351 | 160.872 | 1:16 | 2.309 |
| Feature | BSPT | NPT |
|---|---|---|
| Thread Angle | 55° | 60° |
| Taper | 1:16 | 1:16 |
| Standard | Metric (Europe/Asia) | Imperial (USA) |
How do I know if I am NPT or BSPT?
-
Measure Size and TPI : Check the out diameter or inner diameter , understand the size first and Use a thread pitch gauge to check threads per inch.
-
Check Thread Angle: Use a profile gauge or profile projector ,NPT is 60°, BSPT is 55°.
-
Visual Inspection: NPT threads appear sharper and tapered; BSPT threads are rounder and may be parallel or tapered.
-
Measure Diameter: Take multiple measurements to confirm taper.
Can you fit NPT to BSP?
A common question in industrial piping and hydraulic applications is whether BSPT (British Standard Pipe Tapered) threads and NPT (National Pipe Taper) threads can be used interchangeably. While at first glance both are tapered thread standards with a 1:16 taper ratio, the reality is that mixing BSPT and NPT threads is not recommended due to critical differences in thread angle, pitch, and taper.
Thread Angle Differences
BSPT threads have a 55° thread angle, whereas NPT threads have a 60° angle. This seemingly small difference means that the threads will not fully engage if combined, leading to gaps and uneven contact surfaces. Over time, these gaps can result in leakage, loosening, and mechanical stress on the pipe connections.
Pitch Differences
Another major factor is the thread pitch. For example:
-
1/4″ BSPT thread has 19 TPI (threads per inch)
-
1/4″ NPT thread has 18 TPI
Even though the taper ratio is identical, this pitch difference prevents the threads from aligning correctly. If forced together, the threads will either cross-thread or only partially engage, drastically reducing sealing performance. Pitch misalignment is one of the primary causes of leakage and thread damage in misassembled systems.
Taper and Sealing Compatibility
While both BSPT and NPT use a tapered design to create a mechanical interference fit, the combination of different angles and pitches means the taper profiles do not match. BSPT threads are designed to seal primarily through thread interference, often without sealant, while NPT threads rely on thread interference plus PTFE tape or sealant to achieve leak-free connections. Mixing the two standards eliminates these design benefits and can cause premature failures.
When threads are compatible, the threads fit tightly together
When threads are incompatible, gaps occur between the threads.
Compatibility & Adapters
-
NPT and BSPT threads are not interchangeable.
-
BSPT male threads can sometimes fit BSPP female threads with proper sealing.
-
Use adapters when connecting incompatible threads.
-
Always apply suitable thread sealant and follow installation guidelines.
Plumbing systems that can bring risks, they must avoid using threaded connections. Threads being visible, makes threaded joints weaker, meaning they might have more corrosion and can get fatigue damage quicker because of that possibility being bigger.
hongqian company is NPT pipe fittings suppiler, offering a wide variety of
NPT female thread
NPT male thread
BSPT female thread
BSPT male thread.
In the industry leadership position,hongqian as a professional cnc parts supplier is familar with differnt types of the thread , we have 80 sets cnc lateh machine that professional supply except NPT and BSPT , Alson include
NPTF , M , G , UNF , UNEF , PT ,RP Thread based on customer demand . Want more our company detail , click here !
Related topic :
What does the npt and nptf thread means in hose fittings ?
Different type Threads: Applications, Sizes, and complete guide
