AN fitting sizes?

How do you determine the correct size of AN fittings to use on a model? They have all sorts of sizes of machined fittings, but I don't know what size I should use. If I could see them in life, then it wouldn't be a problem, but anything I can find would be mail-order, and therefore I can't see how big they need to be beforehand. I know I could "divide by 24" but I don't know the original size either. Anyone got a rule of thumb or something I could use?

Hobbylinc has everything listed for detail master fittings. They give a pretty good description of each, there use and the sizes of the turned fittings.
http://www.hobbylinc.com/prods/s_dtm.htm
I haven't used them, I go with R.B. Motion. I think I have a chart in his catalog. I will check after I get home from work.

Well, I thought he had a list for the use of each size, but he didn't.
The basic's as I use them are,

.010-.018 is approx. 3/8-7/16' in 1/24-1/25, good for vac.line and sm. acc. line, sm. fuel line.
.020 is approx. 1/2" , which is good for lg. fuel lines, oil lines,some coolant lines.
.026-.031 is approx. 5/8-3/4", which is good for coolant/heater line, a/c line.
.062-.080-.104 is approx. 1 1/2", 2", 2 1/2" good for rad. hoses.

These are the size for the lines or hose, which would correspond to the hole in the fitting.

As I said, I use R.B. Motion fittings, been using them for a long time and love them. You can e-mail him at [email protected]. Robert will send you a catalog and help you with any questions you may have.

Hope this helps.