Is it a 45 degree automotive flare fitting or a 37 degree aircraft fitting?

 If you're working on older airplanes, or possibly some homebuilts, you might come across a fitting that doesn't look quite right. Is it an automotive 45 degree flare or is it an aircraft 37 degree flare?


Hose fittings

 37 degree or 45 degree?

Here's a quick method:

Draw a right angle onto a piece of paper and place the fitting onto the paper as shown below.

Automotive 45 degree flare fitting 

45 degree flare

45 and 45 makes for a right angle (90 degrees)

37 degree aircraft 

37 degree aircraft AN or industrial JIC flare

If you assemble your own aircraft hoses using hose mandrels you might find my article: Aircraft Hose Assembly - Battle of the Bulge of some interest.


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On some of the pre WWII aircraft they did not have AN fittings, and MS was unheard of. They had Special designed, or Commercial fittings, or AC fittings.

The AC was the design of the day. They are "almost" like AN fittings. I do not recall the degree for the flares or the cones, but I do believe they are different. I do know that on some of them. the thread sizes almost match :-(

just be careful when working on old aircraft, some of the plumbing is just similar enough to be a risk to airworthiness.

ac fittings are at a 35 degree