A straight female flare swivel adapter in AN6, the size most builds use more of than any other. AN6 handles fuel feed and return on the majority of naturally aspirated and moderately boosted engines, along with oil, power steering and transmission cooler lines. The swivel joint lets the 37-degree flare be torqued to a proper seal independently of hose orientation, which saves a great deal of frustration when a fuel rail or filter sits at an awkward angle. It also means the hose is not left wound up against its fittings. Both ends accept standard AN flare connections; verify your components are true 37-degree AN and not a similar-looking alternative seat.