AN Fittings

AN stands for Air Force-Navy Aeronautical Standard and is an aviation fitting standard developed around WWII. The fitting featured a 37 degree mating angle which provided superior sealing compared to the common 45 degree fittings and used a higher class of thread quality. Eventually the AN fittings saw widespread military use and a multiple manufacturers began producing the fittings, leading to quality problems. The Joint Industries Council (JIC), an industry organization, sought to standardize the specifications on this type of fitting and created the "JIC" fitting standard, a 37 degree fitting with a slightly lower class of thread quality than the military AN version. The SAE went on to adopt the JIC standard as well. As a result JIC or SAE 37 degree fittings are perfectly interchangeable with AN fittings, and while this may not be acceptable for military aviation use, for automotive use there is no downside other than perhaps mismatched color coordination as JIC fittings are not available in the pretty anodize aluminum colors. However this may be a worthy tradeoff considering the JIC fittings are a fraction of the price of their true "AN" counterparts

The fittings and adapters seal on the seat and cone and any sealant can cause a poor seat and, therefore, a leak. A lubricating oil should be used on the threads instead of a sealant. Only tapered pipe (NPT) threads require a sealant.

The chart below shows the fitting size, the (accepted) equivalent size, the hose's real inside diameter, and some general uses for the various sizes. Note the General Uses is a guideline only is not meant to be all inclusive; you could use a -32 (2") fuel line if you really wanted to.

When selecting a fitting supplier, each recommend you use only their hoses for their fittings. Also some hoses are to be used with specific type fittings. I suggest you do just that to bypass any fitment or application problems.

Fitting Size Equivalent - O.D. vs. I.D. General Uses
-2 1/8" - 0.125 oil pressure/fuel pressure/vacuum
-3 3/16" - 0.188
(5/32" id - .15625)
oil pressure/fuel pressure/vacuum
-4 1/4" - 0.250
(7/32" id - .2185)
oil pressure/fuel pressure/vacuum
-6 3/8" - 0.375
(11/32" id - .34375)
fuel/transmission/power steering
-8 1/2" - 0.500 - (7/16" id - .4375) power steering/fuel/transmission/heater hose
-10 5/8" - 0.625
(9/16" id - .5625)
fuel/heater hose
-12 3/4" - 0.750
(11/16" id - .6875)
-16 1" - 1.00 - (7/8" id - .875)
-20 1 1/4" - 1.250
(1 1/8" id - 1.125)
radiator hose
-24 1 1/2" - 1.500
(1 3/8" id - 1.375)
radiator hose
-32 2" - 2.00 radiator hose

Three popular players in the AN fitting and pressure hose arena for automotive use are: