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NPT，PT，G都是管螺紋

NPT是National (American) Pipe Thread的縮寫，屬于美國標準的60度錐管螺紋，用于北美地區．國家標準可查閱 GB/T12716。

PT是Pipe Thread的縮寫，是55度密封圓錐管螺紋，屬惠氏螺紋家族，多用于歐洲及英聯邦國家．常用于水及煤氣管行業，錐度規定為1:16．國家標準可查閱GB/T7306。

G是55度非螺紋密封管螺紋，屬惠氏螺紋家族．標記為G代表圓柱螺紋．國家標準可查閱GB/T7307。 另外螺紋中的1/4、1/2、1/8標記是指螺紋尺寸的直徑，單位是英吋．行內人通常用分來稱呼螺紋尺寸，一吋等于８分，1/4吋就是２分，如此類推。G就是管螺紋的統稱(Guan)，55，60度的劃分屬于功能性的，俗稱管圓。即螺紋由一圓柱面加工而成。

ZG俗稱管錐，即螺紋由一圓錐面加工而成，一般的水管接頭都是這樣的，國標標注為Rc。

公制螺紋用螺距來表示，美英制螺紋用每英寸內的螺紋牙數來表示，這是它們最大的區別。公制螺紋是60度等邊牙型，英制螺紋是等腰55度牙型，美制螺紋60度。 公制螺紋用公制單位，美英制螺紋用英制單位。

管螺紋主要用來進行管道的連接，其內外螺紋的配合緊密，有直管與錐管兩種。公稱直徑是指所連接的管道直徑，顯然螺紋直徑比公稱直徑大。1/4，1/2，1/8是英制螺紋的公稱直徑，單位是英寸。

螺紋的角度：公制和美制螺紋都是60度，英制是55度，TM水管螺紋是30度、SM針車螺紋和BC螺紋也是60度、公制梯形螺紋30度、英制梯形螺紋29度、臺形螺紋（TW29度 TR和TM30度）。

普通螺紋：公制螺紋M；英制W；美制UNC、UNE、UNEF

管螺紋：英制PS、PT、PF；美制NPS、NPT、NPTF、NPSM

英制螺紋：按照公稱尺寸和每英寸牙數制定規格. 如1/4"-20,表示公稱尺寸1/4,即大徑為6.35mm（25.4除4=6.35）每英寸20牙，依此類推。

NPT, PT, and G are all pipe threads

NPT is the abbreviation for National (American) Pipe Thread, which belongs to the American standard of 60 degree taper pipe thread and is used in North America. National standards can be found in GB/T12716.

PT is the abbreviation for Pipe Thread, which is a 55 degree sealed conical pipe thread belonging to the Wyeth thread family and is commonly used in European and Commonwealth countries. It is commonly used in the water and gas pipe industry, with a taper specification of 1:16. National standards can be found in GB/T7306.

G is a 55 degree non threaded sealing pipe thread, belonging to the Wyeth thread family. The symbol G represents cylindrical thread. The national standard can be found in GB/T7307. In addition, the 1/4, 1/2, and 1/8 marks in threads refer to the diameter of the thread size in inches. Insiders usually refer to the thread size in minutes, where one inch is 8 minutes, 1/4 inch is 2 minutes, and so on. G is the general term for pipe threads (Guan), and the division of 55 and 60 degrees is functional, commonly known as pipe circles. The thread is machined from a cylindrical surface.

ZG, commonly known as pipe cone, means that the thread is machined from a circular conical surface. Generally, water pipe joints are marked as Rc in the national standard.

Metric threads are represented by pitch, while American and British threads are represented by the number of threads per inch, which is their biggest difference. Metric threads have a 60 degree equilateral profile, British threads have an isosceles 55 degree profile, and American threads have a 60 degree profile. Metric threads are in metric units, while American and British threads are in English units.

Pipe threads are mainly used for connecting pipelines, and their internal and external threads are closely matched, with two types: straight pipes and tapered pipes. The nominal diameter refers to the diameter of the connected pipeline, and obviously the thread diameter is larger than the nominal diameter. 1/4, 1/2, and 1/8 are the nominal diameters of inch threads.

Thread angle: Both metric and American threads are 60 degrees, British threads are 55 degrees, TM water pipe threads are 30 degrees, SM needle thread and BC threads are also 60 degrees, metric trapezoidal threads are 30 degrees, British trapezoidal threads are 29 degrees, and table threads (TW29 degrees TR and TM30 degrees).

Ordinary thread: metric thread M; English W; American UNC, UNE, UNEF

Pipe threads: British PS, PT, PF; American NPS, NPT, NPTF, NPSM

Inch threads: Specifications are established based on nominal size and number of threads per inch For example, 1/4 "-20 represents a nominal size of 1/4, which means a major diameter of 6.35mm (25.4 divided by 4=6.35) with 20 teeth per inch, and so on.