Edelbrock part #3577 Regulator Fitting is a -6 AN fuel inlet fitting is for use with fuel mounted regulators that come included with all Pro-Flo EFI systems. The fitting will screw directly onto the fuel rail mounted fuel regulator and provide you with a -6 AN male nipple to connect your return fuel line to. This is the easiest and cleanest way to connect a return fuel line to your Edelbrock pro-Flo EFI system's fuel regulator.