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NPT,PT,BSP Thread Pipe Fittings Difference and Details

Views: 108     Author: Good Du     Publish Time: 2023-03-08      Origin: Site

       Threaded pipe fittings are used in a particularly wide range of fields, and there are many kinds. For most people, it is impossible to identify all kinds of threads clearly, and the classification of threads is not very clear.  Therefore, mastering the basic knowledge of thread is helpful to facilitate our study and work  in the construction manufacturing industry. This article will take you to understand the types and differences of thread, What are NPT BSP PT ?  What are the differences between Metric Thread, British Standard Whitworth Thread and American Standard Thread?

        A screw thread is a continuous raised spiral linear ridge made by winding in a spiral form around a cylinder or cone.  The thread is divided into internal thread and external thread.  Threaded pipe fittings are fastened or driven by connection of internal and external threads.  The thread is external thread on the outer surface of the workpiece, such as common bolts or screws;  Inside the workpiece is the internal thread, usually on the part to be assembled.  A complete description of the thread should include at least five elements, thread form + nominal diameter + line number + pitch (or lead)+ spin.


Pipe Fitting Thread Types 


Pipe Thread and Standard Thread Conversion Table



Metric or International Standard Thread

Code M, suitable for workpiece connection with diameter of 0.25mm to 300mm, thread angle of 60°, the crest is flat, easy to turn, the root is circular arc, can increase the strength of the thread.  The metric thread has coarse thread and fine thread.


British Standard Whitworth Thread

British Standard Whitworth Thread originated in the United Kingdom, 1841 British citizen Joseph Whitworth invented this thread, hence the name.  This thread has a thread Angle of 55°, the crest and root are circular, also called B.S.W thread.


British Standard Fine Thread

The thread is similar in shape to the B.S.W. thread, also with a 55° thread Angle, but it has more threads per inch,  The less thread thickness for stronger grip, and is used in parts that require high strength roots or need to withstand higher vibration.


American Standard Thread

The crest and root of the American standard thread are flat, with good strength and stress resistance. The thread Angle is 60°, and the specification is expressed by several teeth per inch. It is divided into three grades: coarse thread (NC), fine thread (NF) and extra fine thread (NEF).


Unified Thread

It was developed by the United States, the United Kingdom and Canada, for the commonly used inch thread.  Compared with the American standard thread, the thread Angle is 60°, and the specification is also expressed by the number of teeth per inch, also divided into coarse thread (UNC), fine thread (UNF) and extra fine thread (UNEF)3 grades.


German Standard for DIN Round Thread

It is German DIN standard thread, thread is round, suitable for light bulb, rubber pipe connection, thread code Rd.


Trapezoid Tr Thread

Trapezoidal thread, also called acme thread, it can be adjusted after wear nuts a special drive thread.  The thread Angle is 30° when using metric thread standard, and 29° when using British thread standard.

Common Pipe Threads Mainly Include the Following: NPT BSP PT  

Here I will focus on the NPTThread, NPT is the abbreviation of National (American) Pipe Thread, belongs to the United States standard 60 degree taper pipe thread, NPT thread is a wide range of applications.  NPT thread is general seal cylindrical pipe thread and general seal taper pipe thread. The theoretical position of the reference plane of the American general sealed taper external thread is located in the plane perpendicular to the thread axis and one reference distance (L1) from the small end. 

  • Basic Size:  

    Medium diameter of thread D2=d2=D-0.8*P 

    Thread path size D1=d1=D-1.6*P  

  • Mode of Cooperation:  

    Cylindrical internal thread and taper external thread form a "column/cone" fit;  Conical internal thread and conical external thread form a "cone/cone" fit.  

  • Tolerance  

    The limit deviation of the datum plane axial position of the American seal taper thread is -P +P;  

  • Thread Length  

    The minimum effective thread length of American general sealed taper external thread shall not be less than the actual size of its reference distance + the sum of assembly allowance; 

    The minimum effective thread length of American general sealing thread shall not be less than the sum of the actual deviation of the reference plane position + the basic size of the reference distance + the assembly allowance;  

  • Mark  

    The complete marking of the general seal pipe thread in the United States: thread characteristic code, thread size code and turn code; 

    American general seal taper pipe thread characteristic code: NPT 

    American general seal cylindrical internal thread characteristic code: NPSC


BSP is the general code of British Pipe Thread, but there are three kinds of BSPP, BSPT and BSPF.  BSPP is British cylindrical pipe thread code, only internal thread, equivalent to the domestic 55 degree cylindrical (parallel) pipe thread, and BSPT is a British taper pipe thread standard, refers to the thread thread Angle of 55 degrees, the thread has 1:16 taper, another is BSPF is British fine pipe thread. The front two are used for sealing joint and the back one is used for general joint.

PT is the abbreviation of Pipe Thread, is 55 degrees sealed taper pipe thread, belonging to the Wyeth thread family, mostly used in Europe and federal countries, often used in the water and gas pipe industry, taper 1:16.  The marking of pipe threads consists of thread feature number (R) and dimension number.  R1/2 indicates the R thread with 1/2 thread.


We(Shanghai Zhucheng Pipe Fittings Manufacturing Co Ltd) manufacture pipe fittings include NPT, PT, BSPP, BSPT and BSPF.  The production of threaded pipe fittings are Threaded ElbowThreaded Tee,Threaded Cross,Threaded Coupling,Threaded CapThreaded UnionThreaded NippleSwage Nipple,Hex NipplePlug,Bushing.


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