"AN" (Army-Navy) sizes were established by the Aerospace industry. The AN numbers are equal to the outside diameter, O.D., 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. For example using the table below if you needed a fitting for a 6AN then use a 9/16-18 SAE fitting and you should be all set.

AN Size Metal Tube O.D. Thread Size
2 - 1/8" - 5/16-24 SAE
3 - 3/16" - 3/8-24 SAE
4 - 1/4" - 7/16-20 SAE
5 - 5/16" - 1/2-20 SAE
6 - 3/8" - 9/16-18 SAE
8 - 1/2" - 3/4-16 SAE
10 - 5/8" - 7/8-14 SAE
12 - 3/4" - 1-1/16-12 SAE
16 - 1" - 1-5/16-12 SAE
20 - 1-1/4" - 1-5/8-12 SAE
24 - 1-1/2" - 1-7/8-12 SAE
28 - 1-3/4" - 2-1/4-12 SAE
32 - 2" - 2-1/2-12 SAE