These adapter fittings ease the installation and eliminate the need to stack fittings when connecting your EFi regulator to your fuel rail. Our unique swivel design allows 360-degree rotation after installation and uses our radius port O-Ring connection at the regulator for ultimate flow. For use with regulators with -10 AN ports and fuel rails with 3/8'' NPT. ideal for use with Edelbrock p/n 350-1729 regulator and fuel rail kits with 3/8'' NPT Ports.