This adapter threads into an AN10 male O-ring port and presents an AN6 male 37-degree flare for the hose. It is a big step down, so it is most often used where a large casting such as an oil pan, sump, cooler or fuel cell fitting has only AN10 bosses available but the circuit being plumbed is a modest AN6 feed or return. The port end seals on its O-ring against the boss face rather than on the threads, so there is no sealant to apply and no danger of stressing an alloy casting. Remember the AN6 flare sets the flow ceiling for the whole connection.