Ferrule with plural inner diameters

A tube gripping ferrule for a metal tube fitting, the ferrule comprising:

• a generally cylindrical interior wall through the center of the ferrule so that the ferrule can be installed over a metal tube end;
• the ferrule being case hardened over substantially its entire surface;
• the ferrule is plastically deformed without breaking when completely pulled-up such that a front portion of the ferrule bites into an outer surface of a metal tube end;
• said interior wall comprising first and second cylindrical portions, said first cylindrical portion being axially adjacent a front edge of the ferrule and having the smallest interior wall diameter of the ferrule, said second cylindrical portion having a larger diameter than said first cylindrical portion.