AN fittings

I am trying to find info on AN fittings...... I have no idea what it means when they say -6. I'm lost. Also how do I know which fitting size I need?
Thanks guys

take that size on a 16 as in inch


-4 = 1/4"
-8 = 1/2
-6=3/8"
and so on

AN stands for army navy

Okay thanks man I was completely lost. I knew that it meant army navy, that's all that I knew and it didnt help me at all. lol