a727 lines

Couple of you guys seem unsure on AN, here's the "deal."

In US terms (no metric or British, etc)

there is 37 1/2 degree flare known as AN or in hydraulic usually steel fittings, known as JIC

There is 45 degree flare known as SAE and is the common stuff you find on copper tube, etc. and most automotive stuff. Heavy trucks, might be different.

None of the fittings truely interchange between SAE and AN/ JIC, but some sizes do screw together and some folks "do" interchange them

Two sizes between SAE and AN/ JIC will not interchange, and this is no6, or 3/8, as well as no 12 or 3/4.

There ARE of course other fittings, inverted flare, used on brake lines, etc

The adaptors are available in various stuff, from JIC to JIC, JIC to pipe, JIC to "o ring boss." This is a fitting commonly found in hydraulics which uses a chamfer on the device (cylinder, valve) and the adaptor has an o ring on the shoulder. "O ring boss" is same threads and sizes as JIC

Various hot -rod manufacturers make proprietary special adaptors, such as Holley or other carb adaptors to AN etc.

No6 is the size in 16th of an inch, IE 6/16's or 3/8" nominal. This gets "interesting" as some hose sizes are not truely 3/8, for example commonly used SINGLE braid DIY hydraulic hose. This is commonly (locally) called "Aeroquip" hose because years ago "everybody" used that due to local supply. In this case, "this stuff" might be CALLED no6, but it is generally "one size down" internally, IE no6 is only .31", no 4 is only .19"

And in some cases you might have no6 hose, but with no8 fitting(s) for some reason, (example.)

There is also a certain amount of "bastard" fittings. For example, the common GM power boxes we used to use in our 4x4's used a 3/8 inverted flare for return, but a 3/8 line with a special 7/16 nut for the pressure to prevent mixup. Years later, Weatherhead actually made these in straight, 45, and 90 for guys making up pressure lines. Before that, I used to cut off a 3/8 90, and reflare it with the old 7/16 nut on

Another good example of bastard fittings are at the master cylinder and dist blocks/ prop valves of brake systems, which might use 3/16 tube but a non-standard nut.

MOST original automotive fittings, such as the original flare fittings on your radiator cooler are SAE, NOT JIC.