AN Technical Information

To get your vehicles fluid delivery system plumbed efficiently and quickly, it’s important to know basic information about hoses, hose ends, and adapters.

What is AN thread?

First it’s important to know what this is all about. AN is a military specification dating back to World War II from a joint effort between the Army and the Navy (hence the AN), and was developed to standardize plumbing systems.

AN sizes generally range from -2 to -32 (though it can be scaled higher), with each step equating to the OD (outside diameter) of the tubing in 1/16″ increments. Therefore, a -8 AN would be equal to a 1/2″ OD tube. AN does not specify the ID (inside diameter) of the tubing, so it can vary in thickness. We try to keep our tube wall as thin as possible to permit good flow while still maintaining a strong structure.

AN thread uses a flared fitting, using a 37-degree flare to form a metal-to-metal seal. This is similar to other fittings like JIC, which is an industrial variant of AN. They can be interchangeable, but this isn’t recommended because some specifications can be different and the connection might not be as secure as intended.

Note that AN threads are different for bolts and fittings. In bolts the number refers to the diameter of the bolt whereas in a fitting it refers to the OD of the tube and thereby have different threads. For example, AN6 bolt has a 3/8-24 thread [1] whereas an AN6 fitting has a 9/16-18 thread. 37° AN and 45° SAE fittings and tooling are not interchangeable due to the different flaring angles. Mixing them can cause leakage at the flare.

AN Thread Specifications

AN size-3-4-5-6-8-10-12-16-20
Tube OD3/16"1/4"5/16"3/8"1/2"5/8"3/4"1"1 1/4"
Nominal Hose ID3/16"1/4"5/16"3/8"1/2"5/8"3/4"1"1 1/4"
Actual Hose ID (approximate)1/8"3/16"1/4"5/16"7/16"1/2"5/8"7/8"1 1/8"
SAE thread size3/8-247/16-201/2-209/16-183/4-167/8-141-1/16-121-5/16-121-5/8-12

Torque Specifications

AN fittings seal on the male/female conical flare and over-tightening can damage the seat, causing a leak. Therefore it’s very important to ensure that you are not over-torqueing your AN fittings. We recommend using a small amount of oil on the flare and threads to help smooth things out and limit mechanical contact while still allowing for a leak-free seal.

Listed in this table below are maximum torque specifications. Keep in mind that these are MAXIMUM torque specifications, generally it is recommended to tighten the fitting to hand-tight, then give it another 1/4 turn. If the fitting does not leak or rattle loose, there should be any issues.

AN SizeMaximum Torque Spec (ft-lbs)