Six Types of Commonly Used Aerospace Fittings

Fitting Types

In the aerospace industry,  sections of tubing are usually attached with flared or flareless (compression type) fittings, unlike steel pipes. The SAE Aerospace Standard (AS) establishes the requirements for aerospace fittings that are used in all types of fluid systems. 

Six of the more common thread styles and connections include: 

1. AN 24-degree cone flareless connection fittings and nuts for use in aircraft fluid
   systems at nominal operating pressures up to and including 3000 psi.
2.  AN 37 degree JIC (Joint Industry Council) flared internal cone fluid connection
   fittings for use with 37-degree external cone spherical nose and seal ring fittings are
   used in many types of aerospace fluid systems.
3. O-ring boss (ORB), where a male-threaded part is inserted into a female-threaded
   part, providing a mechanical rubber seal.
4. NPT (National Pipe Thread) providing a leak-free seal without the need for PTFE tape
   or other sealant compounds.
5. Hose barbs, which allow for an easy push-connection of flexible-plastic or rubber
   hose, are not so easily disconnected.
6. Hose clamps used to attach and seal a hose onto a fitting such as a barb or nipple.

Other common fluid connection styles and configurations include:

Bushings, nipples, sleeves, caps, nuts, push-to-connect couplings, crosses, plugs, tees, elbows, reducers, and unions/1.

One important thing to note is that though some aerospace fittings may look identical, no two fittings are the same. The AN (Army-Navy) military standard calls for tighter tolerances and defines all fitting types, whereas the JIC (Joint Industry Council) uses AN specifications as the baseline for their own standards and covers fewer sizes. Though JIC fittings and adapters are very similar to the same size AN, JIC tolerances are more lenient than the comparable AN component. Military-grade AN aerospace fittings are the best choice for critical applications because they provide a superior sealing surface and have tighter dimensional tolerances than JIC fittings. That being said, JIC components are still a reliable choice for less critical applications. 

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Learn more about fittings, get industry insights and read our latest resources in Brennan University. Also, you can read our essential aerospace content here. 

SOURCES:
SAE AS9100c
SAE AS7112
Flight Mechanic 1
Flight Mechanic 2
Hydraulics & Pneumatics
Hose Assembly Tips
Valvers