1. NPT (National Pipe Thread Taper, American National Taper Pipe Thread)

NPT is an American standard taper pipe thread, with a 60° tooth angle and a 1:16 taper design. It is a sealing thread that relies on the deformation of the thread to achieve a sealing effect. It usually needs to be used with raw tape or sealant. NPT threads are widely used in petroleum, chemical, natural gas and high-pressure fluid systems in North America, and are one of the main standards for American standard pipe connections. Common specifications such as NPT 1/2, NPT 3/4, etc. are suitable for occasions that require high sealing. It should be noted that NPT is incompatible with British standard (BSP) threads and cannot be directly mixed.

 

 

2. PT (Pipe Thread Taper, Japanese/Chinese old standard taper pipe thread)

PT is the taper pipe thread code in the Japanese JIS standard and the old Chinese national standard (GB/T 7306-1987). Its tooth angle is 55° and the taper is 1:16, which is the same as the British standard BSPT (R/Rc) thread. PT threads are sealed by taper matching and are usually used for low-pressure to medium-pressure pipe connections, such as water, oil, gas and other systems. Due to the trend of international standardization, PT has been gradually replaced by R (external thread) and Rc (internal thread) in Japanese standards, but it can still be seen on some old equipment in China. Please note that PT threads are incompatible with American standard NPT and cannot be interchanged.

 

3. PF (Parallel Female, Japanese JIS parallel internal thread)

PF is a parallel (straight) internal thread in the Japanese JIS standard (JIS B 0202), with a tooth angle of 55° and no taper. It is a non-sealed thread and usually needs to be used with a tapered thread (such as a PT or BSPT external thread), or rely on auxiliary seals such as gaskets and O-rings. PF threads are mainly used for low-pressure fluid connections, such as hydraulic systems and pneumatic components. Since PF is a straight thread, it has poor sealing when used alone, and must be used with a tapered thread or seal to ensure leakage. When selecting, it is necessary to distinguish between PF (straight thread) and PT (taper thread) to avoid leakage caused by incorrect pairing.

 

4. G (BSPP - British Standard Pipe Parallel, British non-sealed cylindrical pipe thread)

G thread is a British standard (BSPP) straight pipe thread, with a tooth angle of 55° and no taper. It is a non-sealed thread and usually requires a gasket, sealant or O-ring to achieve sealing. G threads are widely used in water pipes, low-pressure gas and hydraulic systems in Europe and Asia, such as G1/2, G3/4 and other specifications. Similar to PF threads, G threads do not have sealing capabilities by themselves and must be used with sealing elements. It should be noted that G threads are not compatible with American standard NPT, but can be used with British standard BSPT (R/Rc) tapered threads, provided that a suitable sealing method is adopted.

 

5. ZG (China's old national standard tapered pipe thread, obsolete)

ZG is the tapered pipe thread code in the old Chinese standard (GB/T 7306-1987), with a tooth angle of 55° and a taper of 1:16. It is functionally the same as the British standard BSPT (R/Rc). ZG threads were once widely used in domestic machinery and piping systems, but due to the trend of international standardization, the new Chinese standard (GB/T 7306-2000) has been replaced with R (external tapered thread) and Rc (internal tapered thread) codes, and ZG threads have now been gradually eliminated. ZG threads may be encountered when repairing old equipment, but internationally accepted R/Rc or NPT standards should be used in new designs to ensure compatibility and availability.

 

Key tips: Improper thread matching is the main cause of leakage. To ensure connection reliability, focus on the following three core elements when selecting: tooth angle (55° or 60°), thread form (taper thread or straight thread) and sealing method (thread deformation seal or auxiliary seal seal). It is recommended that in actual applications, professional thread gauges be used for inspection and verification, or complete thread parameter requirements be provided to suppliers to obtain accurate technical support.