The AN (Army-Navy) fuel fitting standard — equivalent to the JIC (Joint Industry Council) 37° flare standard — is the dominant connection style for high-performance automotive fluid systems, including racing fuel lines, oil cooler hookups, transmission cooler lines, and brake systems on track-only vehicles. The standard was originally developed for military aircraft and has since transferred to the performance automotive aftermarket because of its very high pressure rating, vibration resistance, and ability to be reassembled multiple times without loss of seal integrity.
The AN fitting uses a 37° flared tubing end (distinct from the 45° flare used in HVACR and plumbing) that seats against a matching 37° cone inside the fitting body. A threaded nut draws the flared tube against the cone to create a metal-to-metal seal. The 37° angle provides a longer sealing surface than the 45° flare, which translates into a higher pressure capability and a more positive seal at the cost of slightly more difficult flaring.
Fitting sizes use the AN designation: AN-3, AN-4, AN-6, AN-8, AN-10, AN-12, and so on. The number does NOT correspond directly to a fractional inch dimension — instead, it represents the equivalent tubing OD in 16ths of an inch. So AN-6 corresponds to 6/16" or 3/8" OD tubing, AN-8 corresponds to 8/16" or 1/2" OD, and so on. This sizing convention is universal across the AN/JIC family.
The fitting family includes hose ends (which attach to the end of a flexible hose using a barb and ferrule mechanism), straight nuts and unions, elbows in 45°, 90°, and 180° (return) configurations, tees and crosses for branch lines, bulkhead fittings for clean firewall and bulkhead penetrations, and adapters from AN to NPT, AN to BSP, AN to ORB (O-ring boss), and AN to compression. AN nuts are color-anodized blue or red in many performance applications for visual identification.
Materials are typically C36000 brass or 6061 aluminum for general use, with 304 or 316 stainless steel options for the most demanding applications.