Comprehensive Thread Standards: A Practical Guide

UNC: Unified Coarse Thread 5/16: Nominal Size of the Thread, in Inches 18: Pitch of 1/18, which means 18 threads per inch 3A: Tolerance Grade, Level 3, External Thread (B is for Internal Thread) R.H: Right-Handed

What Are the Differences Between Unified Threads and Metric Threads?

Metric threads are indicated by pitch, while Unified and British threads are indicated by the number of threads per inch, which is their biggest difference. Metric threads have a 60-degree equilateral profile, while British threads have an isosceles 55-degree profile, and Unified threads have a 60-degree profile. Metric threads use metric units, while Unified and British threads use imperial units. Pipe threads are mainly used for connecting pipes, and their internal and external threads fit closely, with straight and tapered pipes being the two types. The nominal diameter refers to the diameter of the connected pipe, and clearly, the major diameter of the thread is larger than the nominal diameter. 1/4, 1/2, and 1/8 are the nominal diameters of imperial threads, measured in inches. The best method is to measure the distance between two thread tips. If it’s an integer or a decimal that can be divided by 5, it is a metric thread. For example: 1MM 1.5MM 1.75MM 2MM 2.5MM 3MM 3.5MM 4MM.

Issues with Tapered British Threads

1. BSP is British Standard Pipe thread. However, there are distinctions like BSP.Tr., BSP.PI., and BSP.F. BSP.Tr. is tapered pipe thread, used for sealing joints. BSP.PI. is parallel pipe thread, used for sealing joints, containing only internal threads, fitting with the external threads of BSP.Tr. BSP.F. is also parallel pipe thread, used for general connections. Just knowing BSP is not enough; detailed confirmation is necessary. Otherwise, if oil or gas leaks, it can be a big problem. 2. Thread G and Thread BSPP are both codes for British cylindrical pipe threads with a thread angle of 55 degrees. 3. How many types of British threads are there? What are the characteristics and representations of BSP threads? There are two types, BSPP (pipe thread) and BSPT (55-degree tapered pipe thread, which is not compatible with the American 60-degree tapered pipe thread NPT). 4. Compare G thread and Rp thread; what are the similarities and differences, and do they have different applications, can they be used interchangeably? G thread and Rp thread are both 55° cylindrical pipe threads. The different codes arise from different countries (organizations). G is the code for China, France, former Soviet Union, and Japan; PF is the code for Japan; BSP and BSPP are the codes for the UK; R and K are the codes for Germany (R is for internal thread, K is for external thread); TPYБ is the code for the former Soviet Union; Rp is the ISO code. 5. What is the difference between 1/8 and NPT 1/8 threads? It should now be the national standard, but in the old NPT standard, it was called Z, which is a 60-degree tapered thread for sealing cylindrical pipe threads, national standard number GB/T12716-2002M; G is a 55-degree non-sealing cylindrical pipe thread, national standard number GB/T3707-2001. 6. Is the English code for British Standard Pipe thread BSP? Does it have a taper? The code should be G, which is a cylindrical pipe thread, without taper. 7. What are the differences between Rp thread and G thread, and can they be used interchangeably? Also, what are the differences between Rp and Rb, and can they be used interchangeably?

Pipe Threads are non-sealing internal and external pipe threads, with the characteristic code G. G1/2 indicates cylindrical internal pipe thread; G1/2A indicates cylindrical external pipe thread. For sealing, the pipe threads are Rp, which indicates cylindrical internal pipe thread; Rc, which indicates tapered internal pipe thread; R, which indicates tapered external pipe thread. Example of thread code: G1/2-LH indicates left-handed internal thread without sealing, with a size code of 1/2 inch. RP and RB cannot be used interchangeably because one is a 55-degree thread and the other is a 60-degree thread.

Are “British Threads” and “Pipe Threads” the Same Thing?

ZG is the first letter of the Chinese pinyin for tapered pipe. It means tapered pipe thread. 3/4 refers to three-quarters of an inch, indicating that the inner diameter of the pipe is 3/4 inch. To be precise, its inner diameter is 19.05 millimeters, but this is an old standard, which is no longer used. The current national standard stipulates that the inner diameter of ZG3/4″ thread is 20 millimeters. Its representation should be: ZG3/4″. Where (” ) is the symbol for inches. One inch equals 25.4 millimeters. One inch equals 8 tenths. The origin of 3/4 is 6/8=3/4, commonly known as 6 points.

Similarly, the inner diameter of ZG1/2″ thread is approximately 15 millimeters, commonly known as 4 points. The inner diameter of ZG1″ thread is approximately 25 millimeters, commonly known as 1 inch. The inner diameter of ZG1.5″ thread is approximately 32 millimeters, commonly known as 1.5 inches. Tapered pipe threads are only used for hydraulic system connections, while pipe threads G3/4″ are only used for water pipe connections. Tapered pipe threads and pipe threads are very similar, with the only difference being the taper. All pipe threads are imperial!!!

Source: CNC Expert

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