AN and NPT Fitting Sizing

We may earn a small commission from affiliate links and paid advertisements. Terms

Originally posted on the now defunct: http://www.geocities.com/chipman_13/AN-NPT.html

AN and NPT Fittings Chart​


"AN" Thread Sizes​

AN sizes, originally developed for use by the U.S. Armed Forces ("A" for Army and "N" for Navy), describe the outside diameter (O.D.) of tubing in 1/16-inch increments. For example, an AN 2 fitting will fit a tube with an O.D. of 2/16", or 1/8", while an AN 8 fitting will fit a tube with an O.D. of 8/16", or 1/2". Because the actual thickness of tube walls can vary from brand to brand, the inside diameter of a tube is not used as a reference. You will also find the dash (-) symbol or the word "dash" itself used in conjunction with AN sizes. A "dash six" fitting translates to AN-6.

Each AN fitting has an established thread sizing. The following chart shows the relationship between AN size, tube O.D., and SAE thread size:

-AN SizeMetal Tube O.D. InchesClosest SAE Thread Size
-21/8"5/16-24
-33/16"3/8-24
-41/4"7/16-20
-55/16"1/2-20
-63/8"9/16-18
-81/2"3/4-16
-105/8"7/8-14
-123/4"1-1/16-12
-161"1-5/16-12
-201-1/4"1-5/8-12
-241-1/2"1-7/8-12
-281-3/4"2-1/4-12
-322"2-1/2-12

"NPT" Thread Sizes​

NPT sizes (National Pipe Taper) are the most commonly used fitting sizes for general plumbing, piping, and tubing use; not quite as popular as AN for automotive use, but still very common. While AN fittings depend on the outside diameter of a tube for sizing, NPT fittings depend on the interior diameter (I.D.) of the fitting itself. The following chart shows the each size's thread-per-inch count, the I.D. of the fitting, and the AN fitting size with the closest-matching I.D.(inside dimension).

NPT SizeThreads Per InchApp. Interior DiameterClosest AN Size
1/16"271/16"2
1/8"271/8"4
1/4"181/4"6
3/8"183/8"8
1/2"141/2"10
3/4"143/4"12
1"11 1/21"16
1-1/4"11 1/21-1/4"20
1-1/2"11 1/21-1/2"24
2"11 1/22"32


NOTE: A thread sealer (such as Teflon Tape or Pipe Dope) is not required when "AN" type fittings are used, but is required for "NPT".
 

Attachments

  • DSC00616.JPG
    DSC00616.JPG
    52.8 KB · Views: 1
Top