1. Overview of Pipe Threads
Pipe threads are a commonly used thread type in industrial pipeline connections, mainly used for connecting pipes, valves, fittings, etc. Common pipe threads include NPT, PT, and G, which follow different standards and are suitable for different regions and applications.
Correctly distinguishing these threads is crucial for ensuring sealing performance and interchangeability, especially in international projects or equipment procurement.
2. NPT Thread
NPT is the abbreviation of National (American) Pipe Thread. It belongs to the American standard 60-degree tapered pipe thread and is mainly used in North America.
2.1 Characteristics
- Thread angle is 60 degrees
- Taper 1:16
- Dry-seal type, sealed by deformation of the thread itself
- National standard: GB/T12716-1991
2.2 Applications
NPT threads are commonly used in pipeline systems in North America, such as in the petroleum, chemical, and natural gas industries.
3. PT Thread
PT is the abbreviation of Pipe Thread. It is a 55-degree sealing tapered pipe thread belonging to the Whitworth thread family and is mostly used in Europe and Commonwealth countries.
3.1 Characteristics
- Thread angle is 55 degrees
- Taper 1:16
- Requires PTFE sealing material
- National standard: GB/T7306-2000
3.2 Applications
PT threads are commonly found in the water and gas pipe industries and are widely used in Europe and Commonwealth countries.
4. G Thread
G is a 55-degree non-thread-sealing pipe thread belonging to the Whitworth thread family, marked as G to represent cylindrical thread.
4.1 Characteristics
- Thread angle is 55 degrees
- Cylindrical thread, no taper
- Non-sealing, requires a sealing gasket
- National standard: GB/T7307-2001
4.2 Applications
G threads are commonly used for low-pressure pipeline connections, such as water pipes and gas pipes, and require a sealing gasket to achieve sealing.
5. Thread Size Markings
Markings such as 1/4, 1/2, and 1/8 in threads refer to the diameter of the thread size, in inches. People in the industry usually refer to thread sizes in “fen”; one inch equals 8 fen, so 1/4 inch is 2 fen, and so on.
G is the general term for pipe thread (Guan). The division into 55 degrees and 60 degrees is functional. It is commonly called pipe round, meaning the thread is machined from a cylindrical surface.
ZG is commonly called pipe taper, meaning the thread is machined from a conical surface. General water pipe fittings are like this, and the national standard designation is Rc.
6. Differences Between Metric, British, and American Threads
Metric threads are expressed by pitch, while British and American threads are expressed by the number of threads per inch. This is their biggest difference.
- Metric thread: 60-degree equilateral thread profile, uses metric units
- British thread: 55-degree isosceles thread profile, uses imperial units
- American thread: 60-degree thread profile, uses imperial units
| Thread Type | Thread Angle | Unit | Standard Example |
|---|---|---|---|
| Metric thread | 60 degrees | Metric | GB/T 192 |
| British thread | 55 degrees | Imperial | GB/T 7307 |
| American thread | 60 degrees | Imperial | GB/T 12716 |
7. Sealing Methods for Pipe Threads
Pipe threads are mainly used for pipeline connections. Their internal and external threads fit tightly, and there are two types: straight pipe and tapered pipe. Nominal diameter refers to the diameter of the connected pipe; obviously, the thread diameter is larger than the nominal diameter.
- NPT: American standard 60-degree tapered pipe thread, dry-seal type, national standard GB/T12716-1991.
- PT: 55-degree sealing tapered pipe thread, sealed with PTFE material, national standard GB/T7306-2000.
- ZG: 55-degree tapered pipe thread, sealed with PTFE material.
8. Selection Recommendations
When selecting pipe threads, factors such as region of use, sealing requirements, and pipe size must be considered. For North American projects, NPT is preferred; for European projects, PT or G is preferred. When sealing is required, choose tapered threads and use sealing materials.
Correct selection can avoid leakage and compatibility issues and ensure safe system operation.