The pipe thread standard is a specification for measuring the size of pipeline connection threads, originating from the British Wyeth thread system in 1841, which converts radial tolerances into axial tolerances through a 1/16 taper. According to the tooth profile angle, it is divided into three categories: British 55 °, American 60 °, and metric 60 °, covering sealed and non sealed types. Common codes include R, G, NPT, etc. When China revised the standards in 2000, the threads of sealed conical pipes were divided into column/cone fit (RP/R1) and cone/cone fit (RC/R2) systems [2-3], while the threads of non sealed cylindrical pipes continued to use the G code [4].
The development of this standard began in 1905 when the United Kingdom issued the first sealing pipe thread standard BS 211. In 1955, the International Organization for Standardization (ISO) proposed the British sealing pipe thread standard (ISO R 7). In 1987, China established the National Thread Standardization Technical Committee (SAC/TC 108) and released the GB/T 7306-2000 standard for sealed pipe threads in 2000 [2-3]. The supporting inspection methods are divided into column/cone inspection (GB/T 22091.1-2008) and cone/cone inspection (JB/T 10031-1999). As of 2021, China has established a thread standard system that is fully in line with international standards.
Pipe threads are divided into the following three categories:
1. British pipe thread (55 °)
Including: general sealed pipe thread (R), non sealed pipe thread (G), old imperial pipe thread from Korea and Japan (PT, PF)
2. American pipe thread (60 °)
Including: general seal pipe threads (NPT, NPSC), dry seal pipe threads (NPTF, NPSF, NPSI, PTF-SAE SHORT), non seal pipe threads (NPSM, NPSL, NPTR, NPSH, NH, NHR)
3. Metric pipe thread (60 °)
Including: general sealed metric pipe threads (MC, MP), non sealed metric pipe threads (M).
Refer to the Manual of Metric, American, and British Thread Standards (Third Edition)
In the old mechanical drawing standards in our country, the thread code for 55 ° sealed conical pipes is ZG, and the thread code for 60 ° general sealed conical pipes is Z,
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One minute understanding of "npt thread"
In China's new mechanical drawing standards, the 55 ° sealing cone pipe thread is changed to column internal thread/cone external thread (RP/R1) [2], cone internal thread/cone external thread (RC/R2) [3]; The general sealing cone pipe thread code for 60 ° is NPT (formulated according to American standards). For details, please refer to the national standard GB/T 7306-2000.
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