Flare fittings are a type of compression fitting used with metal tubing, usually soft steel and ductile (soft) copper, though other materials are also used. Tube flaring is considered to be a type of forging operation,[1] and is usually a cold working procedure. During assembly, a flare nut is used to secure the flared tubing's tapered end to the also tapered fitting, producing a pressure-resistant, leak-tight seal. Flared connections offer a high degree of long-term reliability and for this reason are often used in mission-critical and inaccessible locations.
The tool used to flare tubing consists of a die that grips the tube and a mandrel that is forced into the end of the tube to form the flare by cold working. The most common flare fitting standards in use today are the 45-degree SAE style, and the 37-degree AN style, also used with the JIC system. The AN/JIC style generally has a higher pressure rating for a given size tubing. SAE and AN/JIC fittings are completely incompatible due to the different flare angle. Further, AN fittings (or those complying with subsequent standards) and JIC fittings are not interchangeable for design-controlled applications due to differing quality standards.