This adapter connects 5/8 tube to an AN10 female 37° flare, the size-matched pairing for AN10 plumbing where 5/8″ tube corresponds to the AN10 nominal size. It suits larger fuel feed and return runs, oil cooler circuits and transfer lines where a long section is best executed in rigid tube for protection, cost and appearance, with braided hose used at the flexible ends. The tube must be flared to 37° with the correct tool, not the 45° flare found in general automotive kits. Larger hard line also needs a proper tube bender and adequate clipping to avoid stress at the flare over time.