Flare fitting

Flare fittings are a type of compression fitting used with metal tubing, usually soft steel, ductile (soft) copper and aluminum, though other materials are also used.  Tube flaring is considered to be a type of forging operation, 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. The refrigeration and air conditioning industry usually uses 45° flare connections while hydraulic hoses are usually 37-1/2° flare connections.