This inverted seat adapter joins an AN8 37-degree flare to a 5/8 x 18 inverted flare thread. The 5/8 x 18 seat is the larger of the common inverted flare sizes and turns up on bigger factory hard lines – fuel feed and return on later injected engines, power steering circuits and some hydraulic runs – where a 1/2 x 20 port would be too small for the volume involved. Use it to convert that original port over to braided AN8 hose without re-flaring or replacing the hard line. Both seats are metal to metal, so fit it dry with no tape or sealant. Start the fine thread by hand so it seats square, then tighten firmly without forcing it, and check for weeping under pressure before the car goes back on the road.