The AN6 180-degree PTFE hose end takes the line through a complete U-turn inside the fitting. It comes into its own where a fuel feed or return leaves a rail, regulator or surge tank and has to run straight back alongside itself with no room for a loop. Building the turn into the body protects the PTFE liner, which would kink and restrict if forced into that radius. It seals on an olive squeezed onto the liner by the nipple and can be stripped and rebuilt. Accept that a full reversal costs some flow, and check spanner access around the bend before finalising the layout.