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What Is Pipe Thread?
Pipe threads are specialized threads designed for connections along the walls of pipes. These threads come in two primary types: unsealed 55-degree pipe threads and sealed 55-degree pipe threads. Their main purpose is to ensure a tight fit between internal and external threads when connecting pipes.
There are two main categories of pipe threads: straight and tapered. Straight threads maintain a uniform diameter throughout the length of the pipe, while tapered threads gradually narrow towards one end. Common types of pipe threads include NPT (National Pipe Thread), PT (Pipe Thread), and G (Gas Thread).
NPT, short for National (American) Pipe Thread, is a 60-degree tapered thread adhering to American standards. It's widely used in North America and can be referenced in GB/T12716-1991 for national standards. On the other hand, PT (or BSPT) is a 55-degree sealed conical pipe thread belonging to the Wyeth thread family. It’s predominantly used in Europe and Commonwealth countries, particularly in the water and gas pipe industries, with a taper ratio of 1:16, as per T7306-2000. Domestically, it’s referred to as ZG.
G represents a 55-degree unsealed pipe thread, also part of the Wyeth thread family. This cylindrical thread is denoted by 'G' and can be found in GB/T7307-2001. The markings such as 1/4, 1/2, and 1/8 refer to the diameter of the thread size, measured in inches. Within the industry, these sizes are often expressed in points, where one inch equals eight points, making 1/4 inch equivalent to two points, and so forth. G is the general term for pipe threads (Guan). The distinction between 55 and 60 degrees is functional, commonly known as the pipe circle, meaning the thread is processed on a cylindrical surface.
ZG is commonly known as a pipe cone, meaning the thread is processed on a conical surface. Most water pipe joints follow this design. The national standard is marked as Rc for metric threads, indicating the pitch, while American threads are 60 degrees. Metric units are used for metric threads, whereas imperial units are used for American and British threads. Pipe threads are primarily used to connect pipelines, ensuring tight fits between internal and external threads. There are two types: straight and tapered pipes. The nominal diameter refers to the diameter of the connected pipe, which is always larger than the thread diameter. Measurements like 1/4, 1/2, and 1/8 represent the nominal diameters of inch threads, measured in inches.
The inch pipe thread originates from the inch Wyeth thread. The combination of the Wyeth thread pipeline series and the Wyeth thread profile established the basic size of the inch pipe thread. Based on the 1/16 taper relationship, the radial diameter tolerance of the Wyeth thread was converted into an inch sealed tube tolerance of the axial number of threads (with some rounding and adjustments). Then, based on the tolerance values of the inch sealed pipe thread, the tolerance of the inch unsealed pipe thread was proposed (changing from one-way distribution to one-way distribution, relaxing the top diameter tolerance, and loosening the bottom diameter tolerance). The timeline for the introduction of these three types of threads is as follows:
In 1841, the British Wyeth thread was introduced, and in 1905, the new Wyeth thread standard (BS 84) was released. In 1905, the imperial sealed pipe thread standard (BS 21) was published. From 1905 to 1940, Wyeth Thread handled the responsibility of the imperial unsealed pipe. In 1940, the unsealed pipe thread series (BSP series) of the Wyeth thread was proposed; in 1956, the British unsealed pipe thread standard (BS 2779) was issued separately.
European countries and Commonwealth nations initially adopted the imperial pipe thread standard. The ISO/TC5/SC5 Pipe Thread Standardization Technical Committee and its secretariat are managed by European countries, and the imperial pipe thread standard was adopted by the ISO standard. In 1955, the ISO proposed the inch-sealed pipe thread standard (ISO R 7); in 1961, ISO proposed the standard for imperial unsealed pipe threads (ISO R 228). In 1978, ISO promulgated two official standards for imperial pipe threads (ISO7-1 and ISO228-1). These threads have been widely accepted outside of North America and are extensively used in international trade.
Metric threads are expressed by pitch, while US and British threads are expressed by the number of threads per inch. Metric threads feature a 60-degree equilateral tooth shape, while inch threads have an isosceles 55-degree tooth shape, and American threads have an isosceles 60-degree tooth shape. Metric units (such as millimeters) are used for metric threads, while imperial units (such as inches) are used for US and British threads. “Insiders†often refer to thread sizes in points, where one inch equals eight points, 1/4 inch equals two points, and so on. Additionally, there are ISO-metric thread standards (60 degrees), UN-unified thread standards (60 degrees), API-American Petroleum Institute thread standards (60 degrees), and W-British Whitworth thread standards (55 degrees).
Hebei Sanvo Pipes And Fittings Co., Ltd. is a reputable manufacturer and supplier of high-quality threaded pipe fittings in China, exporting standard NPT, BSPT steel pipe nipples, steel pipe couplings, and 304/316 stainless steel threaded pipe fittings. Our pipe products are available in carbon steel and stainless steel, widely used in fields such as gas, oil and gas, water, fire, HVAC, mines, petroleum, and other fluid transportation. We manufacture according to American Standard ASTM A733/A865, German Standard DIN2982/DIN2986, British Standard BS EN10241, and Japanese Standard JISB2302, selling our products to markets in Israel, Germany, Italy, South Korea, the United States, the Middle East, Canada, France, and beyond, receiving positive feedback.
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