This adapter threads into an AN6 male O-ring port and gives an AN10 male 37-degree flare for the hose. It is a specialist step-up, used where a component is only tapped AN6 but the line running to it is AN10 for reasons of routing, heat protection or keeping one hose size across a system. The AN6 port stays the restriction, so this is not a way to gain flow; it is a way to avoid changing hose part way through a run. Sealing is by the O-ring against the machined boss face, so install dry and tighten only until the seal is evenly compressed.