As a professional manufacturer of various pressure and temperature sensors, BDRTD Platinum Technology has been dealing with various threads for a long time, and is responsible for helping us popularize the knowledge of various threads. (The reference "Metric, American and British Screw Thread Standards Manual (Third Edition)" was prepared by the National Technical Committee for Screw Thread Standardization.)
First, look at a table about thread classification. This is the classification of thread types in the national standard
Now let's talk about the differences between the common M, G, ZG (R, RC) and NPT threads.
1. Metric thread M (60 °)
Metric thread, also known as metric thread, is a commonly used thread in China, and its standard pitch value is specified in the national standard. The standard pitch value of metric screw thread is arranged according to the rule of segmented equal difference sequence, so the speed change mechanism of the screw feed transmission chain is required to change its transmission ratio according to the rule of segmented equal difference sequence. The tooth form of metric thread is 60 degrees, and the pitch refers to the distance between two tooth tips,. Metric thread -- the thread specification parameter is the thread determined in metric unit (mm), which is represented by the nominal size X pitch of M+thread major diameter.
2. British non sealing pipe thread G (55 °)
G, commonly known as pipe thread, is a 55 degree unsealed pipe thread, belonging to Wyeth thread family. The 1/4, 1/2, 1/8 marks in the thread refer to the diameter of the thread size in inches. Professionals often call the thread size "minute". One inch is equal to 8 points, and 1/4 inch is 2 points, and so on.
3. General sealing pipe thread ZG (R, R1 or R2, RC) (55 °)
ZG, commonly known as taper pipe thread, is a very special name, but it is also a kind of thread that is commonly used. It is easy to be confused if it is not sorted out clearly. ZG is a way of expression in the old mechanical drawing standard in China, and has now been changed to R/R1/R2 (external thread), RC (internal thread). There is a special icon at the end to straighten out these relationships of ZG.
4. American thread NPT (60 °)
NPT is the abbreviation of National (American) Pipe Thread. It belongs to the American standard 60 ° general sealing pipe thread. It is used in North America with a taper of 1:16. The 1/4, 1/2, 1/8 marks in the thread refer to the diameter of the thread size in inches. Professionals often call the thread size "minute". One inch is equal to 8 points, and 1/4 inch is 2 points, and so on.
Before 1987, there was no American and British pipe thread standard in China. However, in production, it is impossible to avoid these two internationally widely used pipe thread standards. For this reason, the old mechanical drawing standards once stipulated the marking codes of American and British pipe threads. These thread codes were derived from Chinese phonetic alphabet, and it was not considered whether they were consistent with the foreign standard pipe thread standard codes. Since this standard only specifies the thread code but not the thread parameters, the thread parameters indicated by the same thread code in different enterprises or industries may also be different. There is no basis to judge who is right and who is wrong when scrap occurs. From 1987 to 1991, China issued the British pipe thread standard. From then on, the pipe thread code and mark shall comply with the pipe thread standard. The pipe thread code specified in the old mechanical drawing standards should be abolished immediately.