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Specifications of Threaded Pipe Fittings ASME B16.11

Threaded Pipe Fittings 


Threaded Pipe fittings are the most common method of connecting pipes. Threaded pipe fittings are predominantly used for small pipe diameters, much like Socket Weld Fittings are also used for smaller piping systems. They are generally used for piping with an Outside Diameter (OD) of 2.375-inch (60.3 mm) or smaller that is piping with a nominal diameter of NPS 2 or smaller.
The ASME B1.20.1. document outlines the dimensional standards for tapered pipe threads. It gives all required dimensions which include the pitch diameter, the number of threads per inch, and the normal lengths for all pipe sizes.


NPT Thread (National Pipe Thread)


All the threaded fittings on this site are provided with NPT thread, ASME B1.20.1. The (American) National Pipe Thread, Tapered, is the most widely used thread connection in North America. Threaded pipe fittings are an effective way to seal pipes used for transporting liquids and gases including steam and hydraulic fluid. Due to the taper on NPT threads they form a seal when tightened as the sides of the threads squeeze tight against each other. This is in contrast to straight or parallel threads which only hold the pipe fittings together and do not provide a seal. The thread is tapered 0.75 in/ft (62.5 mm/m), making a larger diameter continually compress into a smaller diameter and this finally forms a seal since no clearance remains between the crests and troughs of the threads due to the taper. As a result NPT fittings should be free of burrs and lubricated using a thread seal tape or lubricating paste like thread seal paste pipe dope. Using tape helps to reduce corrosion and galling on the threads, which could otherwise make future disassembly very difficult.


The Advantages and Disadvantages of Threaded Pipe Fittings



  • Installation is quick and easy
  • Ideal for low-pressure, low-temperature installations with no vibration – prevents leakage in these types of applications.



  • Rapid temperature changes may cause leaks. (Due to the different heat expansion between the pipe and the adjacent fittings.)
  • Excessive Vibration can cause leaks between the threads as they loosen.
  • Not recommended for hazardous piping systems.


Dimensions of National Pipe Thread (NPT)



Common Fittings for threaded pipe systems


  • Hose Barb fittings
  • Connects hose to pipe
  • Close Nipple
  • Connects two Female Threads
  • Hex Nipples
  • Connects two Female threads
  • Full Couplings
  • Connects two Male Threads
  • Pipe Unions
  • Widely used in maintenance to connect two male threads. Consists of three parts, two female threads and a center piece that pulls the ends together when fastened by rotating.
  • Street Elbows
  • Makes a 90° change in the direction of the pipe run.
  • 90° Elbow
  • Makes a 90° change in direction of the pipe run.
  • 45° Elbow
  • Makes a 45° change in the direction of the pipe run.
  • Pipe Tee
  • Makes a 90° branch from the direction of the pipe run.
  • Hex Head Reducing Bushing
  • Reduces or increases the thread size. 
  • Bell Reducer
  • Increases or Decreases the thread size.
  • Hex Head Plug
  • Seals the Female threaded end of a fittings.
  • Square Head Plug
  • Seals the Female threaded end of a fitting.
  • Threaded Cap
  • Seals the male threaded end of a pipe
  • Pipe Flanges
  • Another way to connect pipes and fittings where standardized connections are required
  • Pipe Nipples
  • Threaded pipes af varying lengths


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