what is difference of metric thread,npt thread,pt thread of thread rolling machine

what is difference of metric thread,NPT thread and PT thread of thread rolling machine?

Metric thread is the thread standard in China.

Npt thread is National (American) Pipe Thread , use in North America area, belong to usa standard 60 degree 

PT thread is Pipe Thread, use in Europe and uk, belong the Whitworth thread.

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Metric thread is also called metric thread; Inch thread is also called inch thread; Unified thread is a kind of American thread.

Metric thread, inch thread and American thread are mainly different in pitch, thread size code and thread shape.

The unit of pitch P of metric thread is mm, and its value is generally an integer or a multiple of "5" (including 0.5, 0.05, etc.);

The pitch of inch screw thread and American screw thread is expressed by the number of threads per inch, and n represents the number of threads per inch. The pitch P=25.4/n.

The thread size code of metric thread is the nominal diameter of the thread, generally the major diameter of the thread, in mm.

The thread size codes of inch thread and American thread have different meanings according to different thread types,

The thread code of pipe thread is generally expressed by the nominal size of the pipe, rather than the major diameter, pitch diameter or minor diameter of the thread. The nominal size of the pipe is equal to the inner diameter of the pipe in the old standard, and the nominal diameter of the pipe is generally smaller than the minor diameter of the thread. In the new standard, the nominal size of pipes becomes a dimensionless number, which only represents the code of pipes of a certain specification.

The thread code used for fastening indicates the nominal diameter by the major diameter of the thread, and the unit is inch.

The difference between British thread and American thread is mainly due to the different tooth angle: the tooth angle of British thread is generally 55 °, while that of American thread is generally 60 °.

The tooth profile angle of metric common thread is 60 °, and the feature code of metric common thread is "M".

55 ° pipe thread (including 55 ° non sealing pipe thread and 55 ° sealing pipe thread) in Chinese standard is inch thread, and its thread feature code is "G" or "R".

G is used for 55 ° non sealing pipe thread, which includes internal thread and external thread and is cylindrical thread.

When marking the external thread of 55 ° non sealed pipe thread, the tolerance grade code A or B shall be generally marked;

When marking the internal thread of 55 ° non sealing pipe thread, the tolerance grade code is generally not marked.

For example, G3A represents 55 ° non sealed cylindrical external thread with dimension code 3 and tolerance grade code A;

G3 refers to 55 ° unsealed cylindrical internal thread with size code 3.

The size code 3 indicates that the nominal size of the pipe corresponding to the pipe thread is NPS3, which is equivalent to DN80. The outer diameter of the pipe is generally 89mm. The major diameter D of the pipe thread (55 ° unsealed) is 87.884mm, the pitch diameter D2 is 86.405, and the minor diameter D1 is 84.926mm.

R is used for 55 ° sealing pipe thread. The feature codes of 55 ° sealing pipe thread include Rp, Rc, R1, R2.

Rp represents the internal thread of cylindrical seal;

Rc refers to conical sealing internal thread;

R1 represents the tapered external thread matched with Rp;

R2 represents the conical internal thread matched with Rc.

The size code of 55 ° sealing pipe thread is the same as that of 55 ° non sealing pipe thread.

The 60 ° sealing pipe thread and unified thread in the Chinese standard are American threads.

The characteristic codes of 60 ° sealing pipe thread are "NPT" and "NPSC".

"NPT" means 60 ° sealed taper pipe thread (including internal thread and external thread);

"NPSC" means 60 ° sealed cylindrical pipe thread (only internal thread);

The mark of 60 ° sealing pipe thread consists of thread feature code, thread size code and thread number.

For standard threads, it is allowed to omit the number of threads in the mark.

For example, right handed cylindrical internal threads with size codes of 3/4 and 14 threads are labeled NPSC 3/4-14 or NPSC 3/4.

Unified thread is a kind of thread used for fastening in American system thread.

There are four codes for unified threads:

"UNC" or "UNRC" indicates coarse thread;

"UNF" or "UNRF" means fine thread;

"UNEF" or "UNREF" indicates ultra-fine thread;

"UN" or "UNR" means constant pitch series threads,

If the letter "R" is included in the above four unified thread codes, it means that the minimum arc radius of the external thread root is 0.10825318P.

For unified thread marking, the thread size code and thread number are marked in front of the thread feature code, and the tolerance zone code is marked behind the thread feature code.

For example, for a right-handed constant pitch unified thread with size code of 2 and 12 threads, the tolerance zone of 2A is marked as 2-12 UN-2A.