This adapter takes 3/8 tube and terminates it in an AN6 female 37° flare, which is the matched pairing for AN6 plumbing — 3/8″ tube corresponds to the AN6 nominal size, so the transition from hard line to hose keeps a consistent bore. It is the common choice for fuel feed and return runs where the long chassis section is done in hard line for protection and tidiness, then picked up in braided hose at each end. The tube end must be flared to 37° using the correct flaring tool; a standard 45° automotive flare will not seat correctly against the AN cone and will weep under pressure.