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AN Fittings and Stainless Steel Lines: What size are they, really?

Sometimes we encounter some confusion about the AN specification. This article will explain the AN standard, and explain how our stainless steel lines and AN fittings meet the specification perfectly, as do most of the AN fittings and stainless steel lines sold by our competitors.

Let's start by taking a look at the AN specification. AN (or Army/Navy) was never intended to characterize an entire fluid system, and is mostly designed as a thread specification. AN sizes range from -2 to -32 in irregular steps, with each step equating to the OD (outside diameter) of the tubing in 1/16" increments. This system does not specify the inside diameter of the tubing because the tube wall can vary in thickness.

AN size -2 -3 -4 -5 -6 -8 -10 -12 -16 -20 -24 -28 -32
Tube OD (Hose ID) 1/8" 3/16" 1/4" 5/16" 3/8" 1/2" 5/8" 3/4" 1" 1-1/4" 1-1/2" 1-3/4" 2"
SAE thread size 5/16-24 3/8-24 7/16-20 1/2-20 9/16-18 3/4-16 7/8-14 1-1/16-12 1-5/16-12 1-5/8-12 1-7/8-12 2-1/4-12 2-1/2-12

The following statement applies to all of the braided stainless steel lines on the market that we have measured, as well as our own. If you measure the inside of the PTFE line (or the rubber line in the case of some competing products), you will find that it does not match the Hose ID listed in the table above. There's a perfectly good reason for this. Most importantly, the AN specification was never intended to characterize a fluid system, only a thread type. "Hose ID" in the table above only applies when you are connecting a hose directly to a barb fitting with some type of clamp; it does not apply when you are building a complete line with termination fittings as in the case of braided stainless steel line. This also means that aftermarket braided stainless steel lines are not always interchangeable with other manufacturers line termination fittings.

Why not just make the line bigger so that the ID of the line matches the table, even though it's not required by the AN specification? There's a good reason for this as well. It would be a waste of materials because this type of line requires female fittings, as pictured below:

Because the female end must swivel to screw down onto the male AN fitting, there's no way to keep the ID of the system uniform at the level listed by the AN specification. We've designed the system to be uniform for optimal fluid transfer with no turbulence. If you're convinced that you need a larger line, you can always order the next size up and then use a reducer to change from one AN size to the next. Please check out this table, which lists the actual inner and outer diameters of our lines.

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