A Comprehensive Guide to NPT, BSPP, BSPT, ZG, R, and RC Threads And How To Choose The Correct Thread
1. NPT Threads (National Pipe Tapered)
NPT (National Pipe Tapered) is a U.S. standard for tapered threads used in pipe fittings. These threads create a seal through thread deformation, often requiring thread sealant (like Teflon tape) to prevent leaks.
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Standards: ANSI/ASME B1.20.1
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Angle: 60° thread angle
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Taper: 1°47′ (1.7833°) per side
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Applications: Plumbing, gas lines, hydraulic systems (common in North America)
2. BSPP Threads (British Standard Pipe Parallel)
BSPP (British Standard Pipe Parallel), also known as G threads, feature a straight (parallel) design and rely on a sealing washer or O-ring for leak-proof connections.
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Standards: ISO 228-1, BS 2779
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Angle: 55° thread angle
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Taper: None (parallel threads)
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Applications: Low-pressure hydraulic systems, water and gas fittings (common in Europe and Asia)
3. BSPT Threads (British Standard Pipe Tapered)
BSPT (British Standard Pipe Tapered), or R threads, are tapered like NPT but have a 55° thread angle. They form a seal through thread engagement and often require sealant.
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Standards: ISO 7-1, BS 21
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Angle: 55° thread angle
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Taper: 1°47′ (1.7833°) per side
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Applications: High-pressure hydraulic systems, fuel lines, and pneumatic systems
4. ZG Threads (Metric Tapered Threads)
ZG threads (also called PT threads) are Japanese and Chinese metric tapered pipe threads similar to BSPT but measured in millimeters.
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Standards: JIS B 0203 (Japanese), GB/T 7306 (Chinese)
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Angle: 55° thread angle
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Taper: 1°47′ (1.7833°) per side
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Applications: Hydraulic fittings, industrial equipment in Asian markets
5. R Threads (External Tapered Pipe Threads)
R threads refer to the external tapered threads under the BSPT standard (ISO 7-1). They are designed to mate with Rp (parallel internal) or Rc (tapered internal) threads.
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Standards: ISO 7-1
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Angle: 55°
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Taper: 1°47′
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Applications: High-pressure sealing in oil, gas, and hydraulic systems
6. RC Threads (Internal Tapered Pipe Threads)
RC threads are the internal tapered counterpart to R threads, ensuring a tight seal when paired with external tapered threads.
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Standards: ISO 7-1
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Angle: 55°
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Taper: 1°47′
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Applications: Used in conjunction with R threads for secure sealing in fluid systems
| Feature | NPT | BSPP(G) | BSPT(R) | ZG(PT) | R(External) | Rc(Internal) |
|---|---|---|---|---|---|---|
| Thread Angle | 60 degree | 55 degree | 55 degree | 55 degree | 55 degree | 55 degree |
| Taper | Yes | No | Yes | Yes | Yes | Yes |
| Sealing Method | Thread | O-ring | Thread | Thread | Thread | Thread |
| Standard | ANSI/ASME | ISO 228 | ISO 7 | GB | ISO 7 | ISO 7 |
| Region | South America | Europe | Global | Asia | Global | Global |
How to choose the correct threads ?
Choosing the right thread type—whether NPT, BSPP, BSPT, ZG, R, or RC—depends on regional standards, pressure requirements, and sealing methods. NPT is dominant in the U.S., while BSPP and BSPT are widely used in Europe and Asia. ZG threads are common in Japanese and Chinese applications, and R/RC threads ensure high-pressure sealing in ISO-standard systems.
For leak-free connections, always verify thread compatibility and use appropriate sealants or washers. Understanding these differences ensures optimal performance in plumbing, hydraulic, and pneumatic systems.
Common questions:
Q: Can NPT and BSPT threads be interchanged?
A: No, they have different thread angles (60° vs. 55°) and tapers, leading to potential leaks.
Q: Do BSPP threads need sealant?
A: No, BSPP (G) threads rely on washers or O-rings for sealing.
Q: What is the difference between R and RC threads?
A: R threads are external tapered, while RC threads are internal tapered under ISO 7-1.
By understanding these thread types, engineers and technicians can ensure proper fittings and prevent costly leaks in fluid systems.
When the customers are choosing the suitable threads, please advise the using enviroment , working pressure , or contact our technical department , sales@huiyivalve.com , tel: 0086 18057736259 .