Some widely used pipe fitting standards are as follows:

1. ANSI: The American National Standards Institute ANSI is a private, non-profit organization. Its main function is to administer and coordinate the U.S. voluntary standardization and conformity assessment system. It provides a forum for development of American national standards. ANSI assigns "schedule numbers". These numbers classify wall thicknesses for different pressure uses.

2. ASME: American Society for Mechanical Engineers This is one of the reputed organizations in the world developing codes and standards. The schedule number for pipe fitting starts from ASME/ANSI B16. The various classifications of ASME/ANSI B16 standards for different pipe fittings are as follows:

  • ASME/ANSI B16.1 - 1998 - Cast Iron Pipe Flanges and Flanged Fittings
  • ASME/ANSI B16.3 - 1998 - Malleable Iron Threaded Fittings
  • ASME/ANSI B16.4 - 1998 - Cast Iron Threaded Fittings
  • ASME/ANSI B16.5 - 1996 - Pipe Flanges and Flanged Fittings
  • ASME/ANSI B16.11 - 2001 - Forged Steel Fittings, Socket-Welding and Threaded
  • ASME/ANSI B16.14 - 1991 - Ferrous Pipe Plugs, Bushings and Locknuts with Pipe Threads
  • ASME/ANSI B16.15 - 1985 (R1994) - Cast Bronze Threaded Fittings
  • ASME/ANSI B16.25 - 1997 - Buttwelding Ends
  • ASME/ANSI B16.36 - 1996 - Orifice Flanges etc.

3. ASTM International: American Society for Testing and Materials
This is one of the largest voluntary standards development organizations in the world. It was originally known as the American Society for Testing and Materials (ASTM). This is a reputed scientific and technical organization that develops and publishes voluntary standards on the basis of materials, products, systems and services. This is a trusted name for standards. The standards covered by this organization covers various types of pipes, tubes and fittings, especially made of metal, for high-temperature service, ordinary use and special applications like fire protection. The ASTM standards are published in 16 sections consisting of 67 volumes.

4. AN: Here, "A" stands for Army and "N" stands for Navy The AN standard was originally designed for the U.S. Military. Whenever, a pipe fitting is AN fittings, it means that the fittings are measured on the outside diameter of the fittings, that is, in 1/16 inch increments. For example, an AN 4 fitting means a fitting with an external diameter of approximately 4/16" or ¼". It is to be noted that approximation is important because AN external diameter is not a direct fit with an equivalent NPT thread.

5. BSP: British Standard Pipe BSP is the U.K. standard for pipe fittings. This refers to a family of standard screw thread types for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread. This has been adopted internationally. It is also known as British Standard Pipe Taper threads (BSPT )or British Standard Pipe Parallel (Straight) threads (BSPP ). While the BSPT achieves pressure tight joints by the threads alone, the BSPP requires a sealing ring.

6. Dash (-) size Dash size is the standard used to refer to the inside diameter of a hose. This indicates the size by a two digit number which represents the relative ID in sixteenths of an inch. This is also used interchangeably with AN fittings. For example, a Dash "8" fitting means an AN 8 fitting. A standard hose guide is given below:

     Hose Size In 	Nominal ID Inch Dash Size 	Standard Dash Size
     1/4 	3/16 	-04
     3/8 	5/16 	-06
     1/2 	13/32 	-08
     3/4 	5/8 	-12
     1 	7/8 	-16
     1 ½ 	- 	-
     1 ¼ 	1 1/8 	-20

8. Flanges: Ratings in Classes and Pressure Numbers (PN)

     Flange Class
     	150 	300 	600 	900 	1500 	2500
     Flange Pressure Number, PN
     	20 	50 	100 	150 	250 	420

9. ISO: International Organization for Standardization ISO is the industrial pipe, tube and fittings standards and specifications from the International Organization for Standardization. ISO standards are numbered. They have format as follows:

     “ISO[/IEC] [IS] nnnnn[:yyyy] Title" where
     nnnnn: standard number
     yyyy: year published, and
     Title: describes the subject

10. NPT: National Pipe Thread National Pipe Thread is a U.S. standard straight (NPS) threads or for tapered (NPT) threads. This is the most popular US standard for pipe fittings. NPT fittings are based on the internal diameter (ID) of the pipe fitting.
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