AN vs 45 degree fittings

[travis]

Sorry if this is a newb question, but I really can't seem to find any solid answers.

What are the advantages or disadvantages either way? 45 double flare seems to be by far the most common in OE applications, but the performance aftermarket seems to lean more towards the AN fittings.

I'm building a new fuel system from tank to carb, starting with a Holley in-tank fuel pump with a 1/4" NPT outlet, so I can go either way with the fittings. I'm going with 1/2" lines, so either way I need to buy a larger flaring tool than what I have now.

[bobmc]

I have never double flared fuel lines for carb systems, maybe it's necessary for higher pressure injection systems?

[rebelrouser]

Don't know if there is an engineering reason, but I believe AN fittings were developed for the aircraft industry, and Hot Roders who were exposed to them during WWII in the service, started using them in performance vehicles. And the main reason I double flare all lines on a vehicle is resistance to cracking from vibration. I do know on low pressure applications you can get by with mixing the fittings, but in high pressure like brake lines they will leak.

[54chevkiwi]

I was gonna say the same thing about AN fittings, definitely not needed and so damn expensive

[Alaskaracer]

Depends on what you're using it for. I would never use 45* stuff on a fuel system, only 37*. More expensive, yes. But also seals better than the 45*. Inside the fittings of 45* stuff is sharp corners, sharp turns, and some flow restrictions. 37* stuff has smoother radius, less flow restriction, and more gradual turns. With what your'e doing, AN stuff is a better way to go, especially since you can connect/disconnect easier due to the fittings. To use a 45* flare you have to have a male nut that pushes the flare into the fitting, forcing the seal...on AN stuff, the nut over the flare is female, and also doesn't require nearly as much torque to seal properly, and is easier to disassemble if needed.

[abc]

If you want to go less expensive, you could use JIC fittings if you have a local hardware store with a good selection. JIC and AN will interchange to the untrained eye. AN is held to a tighter manufacturing tolerance than JIC.
SAE 45° seats will also work. I would have to dig into the original engineering of all three to go much further, but for all intended purposes, all three will work for your application. Typically the AN series in the Hot Rod shops is geared and stocked for your exact application.

[amc fan]

AN=Army Navy they have 3A-3B class threads. I do not know if the AN fitting we buy are class 2A-2B threads' JIC standard.
Class 3 thread have a better fatigue life.

[Tom68]

Wheter you double flare or not comes down to the tube you choose, bundy tube is about the only one that'll double flare properly and still seal reliably.

1/2" AN aluminium tube would be single flare with a sleeve, aluminium tube for a fuel line is probably not as good as running flexible fuel rated hose with AN ends.

[1980RS]

When I make a 45° flare it's a double flare, that way I know it's not going to leak. My AN stuff works well also.

[Schurkey]

I have never double flared fuel lines for carb systems, maybe it's necessary for higher pressure injection systems?

If you're using OEM-style double-wall seamless steel tubing and OEM-style inverted flare fittings, it's a legal requirement to double-flare. All the OEM carburetor fuel systems are double-flared when using that tubing, and have been since the middle-sixties; and probably years (decades?) before that.

"AN" and "JIC" are obsolete terms. They've both been replaced by different SAE standards. But the concept is the same--one is "aerospace" grade, and the other is "Industrial" grade.

[bthomas]

May be well known and obvious to some, but my experience is AN fittings are aluminum and jic are steel. Always used AN for lower pressure stuff and jic for things like steering hoses

[Alaskaracer]

May be well known and obvious to some, but my experience is AN fittings are aluminum and jic are steel. Always used AN for lower pressure stuff and jic for things like steering hoses

This is true. JIC is typically used for high pressure hydraulics, AN is used for lower pressure stuff, and for performance stuff....

[nhrastocker]

I have never double flared fuel lines for carb systems, maybe it's necessary for higher pressure injection systems?

"AN" and "JIC" are obsolete terms. They've both been replaced by different SAE standards. But the concept is the same--one is "aerospace" grade, and the other is "Industrial" grade.

Incorrect!
I work for the largest supplier of hardware to the US Military and the AN, MS, NAS, MS, and JIC nomenclatures are still very much in use in the industry.
The US Government purchases under a National Stock Number (NSN), which is a 13-digit code part number assigned to every item repeatedly bought, stocked, used, distributed, and disposed of through the federal supply system. The NSN's, directly convert to AN, NAS, MS, JIC, NAS, or similar part number designation. The SAE Aerospace Spec (AS), just gives the technical specifications for the form, fit, and function of a part.

[bobmc]

I use aluminum tube only, no rust and spark resistant

[jsgarage]

Aerospace AN fittings are red or blue-anodized 6061 aluminum, or shiny stainless steel (may be 413-alloy; can't remember now). Both weld well, as long as you're not concerned about losing the original 3000 psi (>4000 psi burst) pressure rating. A couple of the ss in my stock are welded as-received from the military and the TIG beads are exquisite.

As for sizes, I have one used in aircraft in-flight refueling that's 2-1/2" ID and another used in military jet engines thats 3/16" ID (dash-3) so there are plenty of choices. 45 degree are used in U.S hydraulic and A/C work, and are sometimes brass. As was said, industrial. Mixing 37 and 45 degree angles is always a recipe for disaster.