When flaring aluminum tubing for use with AN fittings, the flare angle must be ________.

• A. 45 degrees
• B. 30 degrees
• C. 40 degrees
• D. 37 degrees

Answer: (D)

The flare angle for aluminum tubing when preparing it for AN (Army-Navy) fittings must be 37 degrees. This specific angle is critical because it ensures a proper fit with the AN fittings, which are designed to seal tightly at this angle. The 37-degree flare creates a conical surface that increases the surface area for the connection, contributing to a more reliable seal and preventing leaks.

Using the correct flare angle is essential in high-pressure fluid systems, where any imperfections in the connection can lead to failure. This is especially important in aviation and automotive applications where safety and reliability are paramount. Other angles, such as 30 or 45 degrees, do not conform to the specifications of AN fittings and could result in inadequate seals or potential damage to the fittings or the tubing itself. This makes the 37-degree flare angle not just a preference but a requirement for effective and safe operation in such systems.