Every thing you wanted to know about A/N fittings

[MDCmotorsports]

Well I figured this needed to be posted sooner or later so....

The AN thread is a particular type of fitting used to connect flexible hoses and rigid metal tubing that carry fluid. It is a US military-derived specification stemming from a joint standard agreed upon by the Army and Navy, hence AN. However, some documents say the name is really Air Force/Navy.

AN sizes range from -2 (dash two) to -32 in irregular steps, with each step equating to the OD (outside diameter) of the tubing in 1/16" increments. Therefore, a -8 AN size would be equal to 1/2" OD tube (8 x 1/16 = 1/2). However, this system does not specify the ID (inside diameter) of the tubing because the tube wall can vary in thickness. Each AN size also uses its own standard thread size.

AN fittings are a flare fitting, using 37° flared tubing to form a metal-metal seal. They are similar to other 37° flared fittings, such as JIC fittings, which is their industrial variant. The two are interchangeable in theory, though this is typically not recommended due to the exacting specifications and demands of the aerospace industry. The differences between them relate to thread class (how tight a fit the threads are) and the metals used.

The "-" in front of the AN fitting is called a "dash" not a negative. If you saw "AN -4" or "-4 AN" you would pronounce A N dash four.

The number after the AN, refer to the size of hose it connects to in 16th's (x/16):

1/8" hose would be 2/16" = DASH 2 OR -2AN
3/16" hose would be 3/16" = DASH 3 OR -3AN
4/16" hose would be 1/4" = DASH 4 OR -4AN
5/16" hose would be 5/16" = DASH 5 OR -5AN
6/16" hose would be 3/8" = DASH 6 OR -6AN
8/16" hose would be 1/2" = DASH 8 OR -8AN

Note that after -6AN, the fittings are of even numbers. -2, -3 & -5 are metric USA conversions.

Moving on for now:

There are 4 types of hoses COMMONLY used in the racing (AN fitting) industry today:

-Rubber

-Kevlar

-Rubber with Stainless Steel shell (see pic below)
-Teflon with Stainless steel shell (see pic below)

There are 3 types of hose ends (fittings) COMMONLY used in the racing (AN fitting) industry today:

-Crimp

-Push Lock
-Threaded

The push lock and threaded types can be found here http://www.goodridge.net/usa/pdf/motorsport/Goodridge_installation_ms.pdf)

Also, I will just go over these:

BSP & NPT

These are typically tapered pipe threads found on turbo charger feeds, oil pressure sending units, and other areas under high pressure.

BSP = British Standard Pipe or metric pipe thread.

NPT = National Pipe Thread or standard pipe thread.

Im sure there's plenty more to add, but this will give all of us a good start for an FAQ on hoses.

 

[silvergsx623]

Wow. thats some great info. I always wondered about the difference.

 

[TobyCat]

I never know how to pronounce half the things out there anyways... Good info MDC.

 

[boostadikt]

nice.... good stuff

 

[suprageezer]

Isn't there a tool/gauge that should be used with ALL AN fittings to acheive the proper tightening specs? I never see anyone mention it or show pics of it.

 

[upgradedsupra]

This is common sense IMO. but not bad for some real newbies I guess.

Duane

 

[jetjock]

There's a lot more to know about it but those basics are a good start. They're old news to anyone who has done aviation maintenance where certified AN is as common as dirt. We've also better hose choices in aviation. Teflon lined with integral fire-sleeving comes to mind.

While there are torque specs for AN fittings the accepted practice is to tighten the B nut 3/4 to one flat after contact. As for JIC it works fine in automotive apps as long as matching fittings are used. Not as pretty as AN but a whole lot cheaper. In fact JIC is mostly what's on my cars even though I get AN for free. It and the even better NAS get saved for more important things.

Btw, I've noticed many automotive people don't use mandrels when assembling hoses. That's a no-no even if they usually get away with it.

 

[drjonez]

some of my notes:

-industrial crimped lines normally have a MUCH smaller ID than comparable assembled fittings....keep that in mind when using them for fueling or turbo oil drains.

-earl's permoflex and autoflex hose seeps fuel vapor.

-aeroquip lines/fittings assemble easiest.

 

[upgradedsupra]

some of my notes:

-industrial crimped lines normally have a MUCH smaller ID than comparable assembled fittings....keep that in mind when using them for fueling or turbo oil drains.

-earl's permoflex and autoflex hose seeps fuel vapor.

-aeroquip lines/fittings assemble easiest.

Good point on that Doc about the industrial fittings.

Duane

 

[Zazzn]

some of my notes:

-industrial crimped lines normally have a MUCH smaller ID than comparable assembled fittings....keep that in mind when using them for fueling or turbo oil drains.

-earl's permoflex and autoflex hose seeps fuel vapor.

-aeroquip lines/fittings assemble easiest.

and so does the Areoquip SS braided lines, they seep vapor as well according to rupinder.

 

[drjonez]

Good point on that Doc about the industrial fittings.

Duane

yup. especially w/the plethora of them offered by various vendors....scary stuff!

and so does the Areoquip SS braided lines, they seep vapor as well according to rupinder.

interesting. which line is he using? i've never had a problem and i'm using the "cheap" AQP stuff.

 

[aljordan]

Also, the flare fittings down at your local hardware store are NOT the same bevel. These are done on a 45 degree bevel whereas AN and JIC is 37 degree. Using these together will not create a proper seal.

Be cautious if a kit comes with brass fittings compared to steel fittings Typically brass fittings are MUCH cheaper and use the 45 degree bevel.

 

[figgie]

since we are brain dumping

The teflon hoses comes in two flavors.

Convoluted hoses Brown and Miller/Icore hose

and smooth bore teflon hoses like the Goodridge 910 smoothbore Teflon hoses

The unfortunate part of both hoses mentioned is a price premium. The advantages.

Compatible with ALL automotive fluids to include Methanol, Ethanol, NirtoMethane, Brake fluid, coolants. No seeping.

<-- runs Progold and goodridge hose all around

 

[jetjock]

Spend a little more and use real aviation stuff. Aeroquip AE701 is a better hose than 601. 666 is teflon lined and impervious to all fuels, oils, alcohols etc. If you don't want the SS braid use 303. None of these will permeate fuel through them. AQ isn't the only one who make MIL-H-83797 hose either. Parkers' Stratoflex 156 is another choice and will fit AN fittings.

 

[figgie]

Spend a little more and use real aviation stuff. Aeroquip AE701 is a better hose than 601. 666 is teflon lined and impervious to all fuels, oils, alcohols etc. If you don't want the SS braid use 303. None of these will permeate fuel through them. AQ isn't the only one who make MIL-H-83797 hose either. Parkers' Stratoflex 156 is another choice and will fit AN fittings.

since you are in the aviation industry still

know of anyone off hand that makes the AN hose fittings in a MALE format instead of a female format? SAve from buying the fitting and the hose fitting

 

[Reign_Maker]

I just skimmed this, I gotta go back and read this, but damn Jon, I needed this info a week ago, hell, I STILL need it, lol... I gotta sticky this or something... This is definately some info we all could use when upgrading... Those fittings are confusing as hell...

 

[Justin]

Those fittings are confusing as hell...

Uh, YES.

I know they're second nature to you guys, but I'm still learning about all this fun stuff I'm glad everyone is chipping in to make it all more understandable.

 

[figgie]

yup. especially w/the plethora of them offered by various vendors....scary stuff!



interesting. which line is he using? i've never had a problem and i'm using the "cheap" AQP stuff.

FYI

THE AQP might be "cheap" price wise but the hose itself is an "elastometer" based hose and not rubber.

Aeroquip rate the hose as GOOD for Gasoline and EXCELLENT for Ethanol (E85) (Fourth Value). I am starting to wonder if the seepage is just from not properly building the hose.. Must investigate!

1 Nitrile, 2 PTFE, 3 ThermoPlastic, 4 AQP, 5 Special App hose, 6 EPDM.
Ratings: E = Excellent, G = Good, C=Conditional, U = Unsatisfactory


Ethyl Alcohol (Ethanol) E E C E E E E E E C C E E E G E
Gallic Acid, Solution G E &#8211; C G G G G E U &#8211; U &#8211; G C G
Gasoline C E E G U E C U E E E E E E E E
Gasohol C E G C U G G U E E E E E E G E