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AN thread

AN thread

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The AN thread is a particular type of fitting used to connect flexible hoses and rigid metal tubing that carry fluid. It is a US military-derived specification that dates back to World War II and stems from a joint standard agreed upon by the Army and Navy, hence AN.

AN sizes range from -2 (dash two) to -32 in irregular steps, with each step equating to the OD (outside diameter) of the tubing in 1/16" increments. Therefore, a -8 AN size would be equal to 1/2" OD tube (8 x 1/16 = 1/2). However, this system does not specify the ID (inside diameter) of the tubing because the tube wall can vary in thickness. Each AN size also uses its own standard thread size.

AN fittings are a flare fitting
Flare fitting
Flare fittings are a type of compression fitting used with metal tubing, usually soft steel and ductile copper, though other materials are also used.  Tube flaring is considered to be a type of forging operation, and is usually a cold working procedure.  During assembly, a flare nut is...

, using 37° flared
Flare fitting
Flare fittings are a type of compression fitting used with metal tubing, usually soft steel and ductile copper, though other materials are also used.  Tube flaring is considered to be a type of forging operation, and is usually a cold working procedure.  During assembly, a flare nut is...

 tubing to form a metal-metal seal. They are similar to other 37° flared fittings, such as JIC
JIC fitting
JIC fittings, defined by the SAE J514 and MIL-F-18866 standards, are a type of flare fitting machined with a 37-degree flare seating surface.  JIC fittings are widely used in fuel delivery and fluid power applications, especially where extremely high pressure is involved.  The SAE J514...

, which is their industrial variant. The two are interchangeable in theory, though this is typically not recommended due to the exacting specifications and demands of the aerospace industry. The differences between them relate to thread class and shape (how tight a fit the threads are), and the metals used.

Note that 37° AN and 45° SAE fittings and tooling are not interchangeable due to the different flaring angles. Mixing them can cause leakage at the flare.

Originally controlled by the specification MS33656, but is now controlled by SAE-AS4395.
Size comparison
AN size -2 -3 -4 -5 -6 -8 -10 -12 -16 -20 -24 -28 -32
Tube OD (Hose ID) 1/8" 3/16" 1/4" 5/16" 3/8" 1/2" 5/8" 3/4" 1" 1-1/4" 1-1/2" 1-3/4" 2"
SAE thread size 5/16-24 3/8-24 7/16-20 1/2-20 9/16-18 3/4-16 7/8-14 1-1/16-12 1-5/16-12 1-5/8-12 1-7/8-12 2-1/4-12 2-1/2-12
Pipe thread size (NPT) 1/8-27 1/4-18 3/8-18 1/2-14 3/4-14

See also

  • Flare fitting
    Flare fitting
    Flare fittings are a type of compression fitting used with metal tubing, usually soft steel and ductile copper, though other materials are also used.  Tube flaring is considered to be a type of forging operation, and is usually a cold working procedure.  During assembly, a flare nut is...

  • National pipe thread
    National pipe thread
    National Pipe Thread Tapered Thread is a U.S. standard for tapered threads used on threaded pipes and fittings. The taper rate for all NPT threads is measured by the change of diameter over distance. The angle between the taper and the center axis of the pipe is 1° 47′ 24″...

  • O-ring boss seal
    O-ring boss seal
    An O-Ring boss seal is a technique for joining two fluid-carrying pipes, hoses or tubing. In an o-ring boss system, a male threaded part is inserted into a female threaded part, providing a mechanical seal...

  • Swage
    Swage
    Swaging is a forging process in which the dimensions of an item are altered using a die or dies, into which the item is forced. Swaging is usually a cold working process; however, it is sometimes done as a hot working process....

  • Threaded pipe
    Threaded pipe
    A threaded pipe is a pipe with screw-threaded ends for assembly.- Tapered threads :The threaded pipes used in some plumbing installations for the delivery of gases or fluids under pressure have a threaded section that is slightly conical . This is called a "tapered thread"...


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