Development History

Inch pipe threads are derived from Inch Wyeth threads, and the Wyeth thread line series and Wyeth thread form combinations establish the basic dimensions of inch pipe threads. In 1/16 taper relationship, the radial diameter tolerance of the Wyeth thread is converted to the axial tolerance of the inch seal pipe thread (there is a certain amount of trim and adjustment). Referring to the tolerance value of the inch seal pipe thread, the tolerance of the inch unsealed pipe thread is proposed (the tolerance is changed from one-way distribution to one-way distribution, the top diameter tolerance is relaxed, and the bottom diameter tolerance is released). The time for the three threads is:

In 1841, the British Wyeth thread was proposed. In 1905, the new Wyeth thread standard (BS 84) was issued.

In 1905, the British Standard Sealed Pipe Thread Standard (BS 21) was issued.

From 1905 to 1940, the Wyeth thread fulfilled the duties of the British non-sealed tube. In 1940, the Wyeth thread unsealed pipe thread series (BSP series) was proposed; in 1956, the British non-sealed pipe thread standard (BS 2779) was issued separately.

European countries and Commonwealth countries first accepted the British pipe thread standard. The ISO/TC5/SC5 Pipe Thread Standardization Technical Committee and its secretariat are controlled by European countries, and the British Pipe Thread Standard is adopted by the ISO standard. In 1955, ISO proposed the British Standard Sealed Pipe Thread Standard (ISO R 7); in 1961, ISO proposed the British Unsealed Pipe Thread Standard (ISO R 228). In 1978, ISO promulgated two official standards for inch pipe threads (ISO7-1 and ISO228-1). Inch pipe threads have been widely accepted by countries outside North America and are widely used in international trade.

Inch pipe threads in the ISO standard have been converted to metric units. The metric method of the inch pipe thread is very simple. Multiply the inch size of the original pipe thread by 25.4 to convert it to the millimeter size. The problem of the inch pipe thread size being eliminated. It is unrealistic to use a true pipe thread standard. There are no points between the true rice pipe thread and the fake rice pipe thread.

Inch seal pipe threads are available in two ways: "column/cone" and "cone/cone". The two inch seal pipe threads use different thread ring gauges (cylindrical thread ring gauge and taper thread ring gauge) and thread plug gauges (the position of the reference plane is different, the two reference planes are half a tooth away from each other). European countries mainly use "column/cone" with thread, while countries outside Europe mainly use "cone/cone" with thread.

For the same sealed pipe thread, the pipe thread that has passed the inspection in European countries may not be qualified in the test outside Europe. In international trade, we must pay attention to this difference, otherwise there may be waste. Prior to 1994, ISO's Inch Sealed Pipe Thread Standard and its gauge standards were designed in accordance with the "cone/cone" fit system. China's British sealed pipe thread products can enter the international market directly. Pipe thread products of pipe threads in European countries are at a disadvantage. After 2000, ISO's Inch Sealed Pipe Thread Standard and its gauge standards were designed according to the "column/cone" matching system. China's original British sealed pipe thread products will encounter difficulties in entering the international market. To this end, China revised the national standard for inch sealed pipe threads in 2000. Changing the original thread standard to two thread standards reminds the designer to pay attention to the difference and correct selection of the two mating threads. When Japan revised the British standard seal pipe thread standard in 1999, it still insisted on adopting the ISO standard before 1994. Therefore, the international British sealed pipe thread market after 2000 is more complicated, and domestic manufacturers should be careful.