NPT，PT，G都是管螺纹

NPT是National (American) Pipe Thread的缩写，属于美国标准的60度锥管螺纹，用于北美地区．国家标准可查阅 GB/T12716。

PT是Pipe Thread的缩写，是55度密封圆锥管螺纹，属惠氏螺纹家族，多用于欧洲及英联邦国家．常用于水及煤气管行业，锥度规定为1:16．国家标准可查阅GB/T7306。

G是55度非螺纹密封管螺纹，属惠氏螺纹家族．标记为G代表圆柱螺纹．国家标准可查阅GB/T7307。 另外螺纹中的1/4、1/2、1/8标记是指螺纹尺寸的直径，单位是英吋．行内人通常用分来称呼螺纹尺寸，一吋等于８分，1/4吋就是２分，如此类推。G就是管螺纹的统称(Guan)，55，60度的划分属于功能性的，俗称管圆。即螺纹由一圆柱面加工而成。

ZG俗称管锥，即螺纹由一圆锥面加工而成，一般的水管接头都是这样的，国标标注为Rc。

公制螺纹用螺距来表示，美英制螺纹用每英寸内的螺纹牙数来表示，这是它们最大的区别。公制螺纹是60度等边牙型，英制螺纹是等腰55度牙型，美制螺纹60度。 公制螺纹用公制单位，美英制螺纹用英制单位。

管螺纹主要用来进行管道的连接，其内外螺纹的配合紧密，有直管与锥管两种。公称直径是指所连接的管道直径，显然螺纹直径比公称直径大。1/4，1/2，1/8是英制螺纹的公称直径，单位是英寸。

螺纹的角度：公制和美制螺纹都是60度，英制是55度，TM水管螺纹是30度、SM针车螺纹和BC螺纹也是60度、公制梯形螺纹30度、英制梯形螺纹29度、台形螺纹（TW29度 TR和TM30度）。

普通螺纹：公制螺纹M；英制W；美制UNC、UNE、UNEF

管螺纹：英制PS、PT、PF；美制NPS、NPT、NPTF、NPSM

英制螺纹：按照公称尺寸和每英寸牙数制定规格. 如1/4"-20,表示公称尺寸1/4,即大径为6.35mm（25.4除4=6.35）每英寸20牙，依此类推。

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.