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Fitting Flare Angle AN Aircraft Flare fittings have a 37 degree flare angle. Many industrial fittings use a 45 degree flare angle. Most of the time, when you are working on aircraft, the hoses have a 37 degree flare and you don't think about the flare angle. You need to make sure that you are not screwing a hose with a 45 degree industrial fitting into a 37 degree aircraft. You might also run across an air conditioning hose that has a 45 degree industrial fitting on one end and an aircraft 37 degree on the other. Be sure that the 45 mates to 45 and 37 mates to 37. Both male and female threads need to be the same angle for a leak-tight seal. How do you tell them apart? The pictures show how you can draw a right angle and place the nipple against the lines. The flare surfaces of a 45 degree fitting will parallel the lines as the picture shows. A 37 degree flare fitting will not line up with your right triangle.

Twist Angle

When both fittings on a hose are angled fittings and the fittings go off in different directions, the angular relationship between fittings is termed the compound twist angle. Twist angle is determined by the number of degrees between the fittings. Point the fitting closest to you toward the floor. Extend the hose out away from your body. Compare the direction that the far fitting is pointing to the chart below:

The twist angle on the hose above is 270 degrees.