You definately do not need -10 size fuel lines, neither supply nor return. Remember, the system is only as good as your smallest restriction. This being the factory engine fuel rail. Unless your going over 500 H.P., a -6 supply & return should suffice. The factory sizing at the fuel rail connections are: supply-3/8"...return-5/16". Same sizing on the Corvette fuel filter/regulator. My .02