AN Plumbing Info and Thread Chart

"AN" aka Army-Navy 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. The sizes range from -2 (dash two) to -32 in irregular steps. The numbers are equal to the outside diameter [OD] of the tubing in 1/16". Since tubing and hoses can have different wall thicknesses, the size number does not necessarily tell you how large the inside diameter will be.

Each AN size number has its own standard thread size [see column three of the chart].   These are the same thread sizes that have been used in aircraft and industrial applications for many years. The flare standard is unique since its 37º flare where normal flare is 45º. So AN fittings have to connect to AN fittings, there is no interchanging the two. 
 AN Size Metal Tube O.D. and Common I.D. Thread Size
2 1/8" or 0.125
5/16-24 SAE
3 3/16" or 0.1875
3/8-24 SAE
4 1/4" or 0.25
7/16-20 SAE
5 5/16" or 0.3125
1/2-20 SAE
6 3/8" or 0.375
9/16-18 SAE
8 1/2" or 0.5
3/4-16 SAE
10 5/8" or 0.625
7/8-14 SAE
12 3/4" or 0.75
1-1/16-12 SAE
16 1"
1-5/16-12 SAE
20 1-1/4" or 1.25"
1-5/8-12 SAE
24 1-1/2" or 1.5"
1-7/8-12 SAE
28 1-3/4" or 1.75"
2-1/4-12 SAE
32 2"
2-1/2-12 SAE