AN thread

The AN thread (also A-N) is a particular type of fitting used to connect flexible hoses and rigid metal tubing that carry fluid.

It is a US military-derived specification that dates back to World War II and stems from a joint standard agreed upon by the Army Air Corps and Navy, hence AN.

The Air Corps-Navy involvement is also the origin of the red/blue color combination that was traditionally used in the anodized finishing process.

[2] The two are interchangeable in theory, though this is typically not recommended due to the exacting specifications and demands of the aerospace industry.

Although similar, 37° AN and 45° SAE fittings and tooling are not interchangeable due to the different flare angles.