AN Fittings & Fitting Adapters
The “AN” in AN Fittings refers to “Army/Navy”. AN fittings were the agreed upon standard by the military for hoses carrying liquids and gasses. It’s a set of sizes and sealing methods, making plumbing universal across different branches of the military.
AN fittings and hoses are often found installed on high performance and race cars. AN hoses are used for fuel, oil, coolant and hydraulic fluids. They are often used in aviation but like most high performance aviation equipment they eventually ended up on race cars and then street cars.
People use AN fittings because they look cool and provide a secure fitting that seals hoses better than traditional push on nipples and hose clamps. They form a serviceable connection that provides a reliable seal.