Pipe threads are specialized for sealing and pressure resistance in piping systems. They are categorized into American, British, and other standards. Below are details on classifications, standards, and differentiation methods:
I. Pipe Thread Classifications & Standards
1. American Standard Pipe Threads :
NPT (National Pipe Taper) : NPT (National Pipe Thread Tapered) is a US standard tapered pipe thread, widely used in North American piping systems for sealed connections of liquids and gases. Its standard is defined by the ANSI/ASME B1.20.1 specification. Taper design: The thread has a taper of 1:16 (1/16 inch change in diameter per inch of length), and the seal is achieved by squeezing the internal and external threads when tightening. Thread angle: The thread angle is 60°, which is different from the 55° of the British BSP thread. Dimensioning: Indicated by nominal diameter (such as 1/2 inch) and number of threads per inch (such as 14 threads), for example “1/2-14 NPT”.
NPS (National Pipe Straight) :NPS (National Pipe Straight, also known as National Pipe Straight Mechanical) is a US standard straight pipe thread. It is a non-sealing thread and is mainly used for mechanical connection rather than pressure sealing. Its standard is defined by ANSI/ASME B1.20.1, which is the same as the NPT thread fitting, but the design purpose is different. Straight thread design: no taper (parallel threads), relying on the mechanical bite of the thread itself to achieve connection, not relying on taper sealing. Thread angle: the same as NPT, the tooth angle is 60°. Sealing method: additional gaskets, O-rings or sealants are required to assist in sealing (it cannot achieve pressure sealing by itself). Dimensioning: Similar to NPT, marked with nominal diameter and number of threads per inch, such as “1/2-14 NPS”.
NPTF (Dryseal) :NPTF (National Pipe Thread Tapered Fuel) is a standard dry-seal tapered pipe thread in the United States. It is an improved version of NPT thread and is designed for seals without sealants. It is suitable for leak-proof scenarios of high-pressure, flammable or hazardous fluids. Its standard is defined by the ANSI/ASME B1.20.3 specification. Taper design: Same as NPT, with a 1:16 taper, and sealing pressure is generated by the tapered fit of internal and external threads. Thread improvement: The top of the tooth contacts the root of the tooth. The top of the tooth (external thread) and the root of the tooth (internal thread) of the NPTF thread are precisely machined to form a line contact between the metals to prevent fluid penetration. Interference fit: The thread profile is slightly larger than NPT. During installation, the gap is filled by slight deformation to achieve “dry sealing”. Thread angle: The tooth profile angle is 60°, which is consistent with NPT. Dimensioning: Same as NPT, for example “1/2-14 NPTF”.
2.British Standard Pipe Threads :
BSPP (G Series, Parallel) : BSPP (British Standard Pipe Parallel) is a British standard straight pipe thread, which is a non-tapered sealing thread and is widely used in Europe, Asia and other regions. Its standards are defined by ISO228-1 (international standard) and BS2779 (British standard). Its core function is mechanical connection, which requires gaskets to achieve sealing. Straight thread design: no taper (parallel thread), leak-proof through gaskets or end face sealing. Thread angle: The tooth angle is 55°, which is different from NPT’s 60°. Sealing mechanism: A flat gasket or O-ring (such as a sealing structure that complies with ISO 1179) is required to fill the end face gap. Dimensioning: Expressed in nominal diameter (such as G1/2), for example “G1/2 BSPP” or “Rₚ1/2” (old marking).
BSPT (R/P Series, Tapered) :BSPT (British Standard Pipe Tapered) is a British standard tapered pipe thread. It is a sealing thread and is widely used in pipeline systems in Europe, Asia and other regions. Its standards are defined by ISO 7-1 (international standard) and BS 21 (British standard) specifications, and sealing is achieved through taper fit and sealant. Taper design: A 1:16 taper (the same as NPT) is used to generate sealing pressure through the tapered extrusion of internal and external threads. Thread angle: The tooth angle is 55°, which is different from the 60° of NPT. Sealing mechanism: Relying on taper fit (metal-to-metal contact) + sealant (such as raw tape or sealant) to fill the gap to achieve leak-proof. Dimensioning: Expressed in nominal diameter (such as G1/2), for example “G1/2 BSPT” or “Rc (internal thread) / R (external thread) + size”.
3.Other Standards :
JIS (Japanese) : JIS (Japanese Industrial Standards) is a national standard system developed by the Japan Industrial Standards Commission (JISC), covering multiple fields such as machinery, electronics, chemicals, construction, materials, etc. It aims to unify the quality, testing methods and safety specifications of domestic industrial products in Japan and promote technical compatibility and international trade.
PT:Tapered (1:16, 55°), e.g., PT1/2.PT thread (Pipe Thread Tapered) is a tapered pipe thread in the Japanese Industrial Standard (JIS), mainly used for sealing pipe connections. Its standard is defined by JIS B 0203. The PT thread design combines taper and precision tolerance, and is suitable for the leakage prevention needs of medium and low pressure fluid systems such as liquids and gases.
PS:Parallel threads.
DIN 2999:Tapered (compatible with BSPT).DIN 2999 is a British taper pipe thread defined in the German Industrial Standard (DIN) for sealed pipe connections. Its design is based on the British standard BSPT (ISO 7-1), but the marking method and some parameters follow the German specifications. This standard has now been replaced by DIN EN 10226 (equivalent to ISO 7-1), but it may still be encountered in old equipment or literature. Thread type: Tapered pipe thread (Tapered Thread), taper is 1:16 (same as BSPT and NPT). Thread angle: 55°, in line with the British standard (BSPT), different from the 60° of the American standard NPT. Sealing mechanism: relying on taper fit + sealant (such as raw tape or sealant) to fill the gap to achieve leakproofness. Dimension marking: Use the British standard code (such as “Rc 1/2” for internal thread and “R 1/2” for external thread), but marked as DIN 2999 standard.
DIN 3852:Parallel (similar to BSPP).DIN 3852 is a straight pipe thread defined in the German Industrial Standard (DIN). It is a non-sealing thread and is mainly used for mechanical connections. It needs to be sealed by an end gasket or O-ring. Its design is compatible with the ISO 228-1 (BSPP) standard, but the marking method and some tolerances follow the German specification. Straight thread design: no taper (parallel threads), relying on end seals to prevent leakage. Thread angle: The tooth angle is 55°, which is consistent with the British standard BSPP, and different from the 60° of the American standard NPS. Sealing mechanism: It needs to be used with a flat gasket or O-ring (in accordance with the ISO 1179 standard) to achieve end face sealing. Dimension marking: Indicated by nominal diameter and thread type, such as “G1/2 DIN 3852” or “Rp 1/2” (old marking).
II. Differentiation Methods
1.Taper vs. Parallel :
Tapered threads (NPT, BSPT) decrease in diameter toward the end (1:16 taper).Parallel threads (BSPP, NPS) maintain constant diameter.
2.Thread Angle & Pitch : American:60°; British/Japanese:55°.Measure TPI (e.g., 1/2″ NPT = 14 TPI).
3.Markings : American:NPT, NPS, NPTF. British:G (parallel), R/Rp/Rc (tapered). Japanese:PT/PS.
4.Sealing Mechanism : NPT/BSPT: Taper compression + sealant. BSPP/NPS: Gaskets required. NPTF: Interference fit (sealantfree).
Thread Type Comparison Table
| Feature | NPT | NPS | BSPP | BSPT | DIN 2999 | DIN 3852 |
| Standard | US (ANSI/ASME B1.20.1) | US (ANSI/ASME B1.20.1) | UK (ISO 228-1/BS 2779) | UK (ISO 7-1/BS 21) | German Legacy (≈ ISO 7-1) | German (DIN 3852) |
| Thread Type | Tapered (Sealing) | Straight (Non-sealing) | Straight (Non-sealing) | Tapered (Sealing) | Tapered (Sealing) | Straight (Non-sealing) |
| Thread Angle | 60° | 60° | 55° | 55° | 55° | 55° |
| Taper | 1:16 | None | None | 1:16 | 1:16 | None |
| Sealing Mechanism | Taper compression + sealant | Gasket/O-ring | Face seal (gasket/O-ring) | Taper compression + sealant | Taper compression + sealant | Face seal (gasket/O-ring) |
| Typical Marking | 1/2-14 NPT | 1/2-14 NPS | G1/2 BSPP | G1/2 BSPT (Rc/R) | Rc 1/2 DIN 2999 | G1/2 DIN 3852 |
| Application | Medium/high-pressure fluid sealing (US equipment) | Mechanical joints (low-pressure US systems) | Low-pressure fluid (EU/Asia equipment) | Medium/high-pressure fluid (EU/Asia equipment) | Legacy German equipment (obsolete) | Low-pressure joints (German equipment) |
| Compatibility | Incompatible with BSPT/BSPP | Incompatible with BSPP | Compatible with DIN 3852 | Incompatible with NPT/BSPP | Compatible with BSPT/ISO 7-1 | Compatible with BSPP |
III. Compatibility
- NPT vs. BSPT:Incompatible (60° vs. 55°).
- BSPT (R) + BSPP (G):Possible with sealant.
- Solutions:Use adapters (e.g., NPTtoBSPT) or match standards.
IV. Application Recommendations
- Hydraulics (High Pressure):NPTF or BSPT.
- Water/Gas (Low Pressure):NPT/BSPP with sealant.
- Chemical Piping:BSPP (stainless steel) + fluoropolymer gaskets.
Summary
Pipe threads vary by angle, taper, markings, and sealing methods. Correct identification ensures leakfree connections. Always verify with thread gauges or manufacturer specifications to avoid mismatches.