Cobra Men's Fly Z Black 7/1 Combo Iron Set, Graphite Hybrids with Steel Irons, Stiff, 3-4H, 5-GW, Right Hand, 3-4H Speed Channel Sole: Key area of the sole is engineered to flex during impact Speed Channel Face: An engineered trench behind the face area helps to minumize face thickness and increase flexion Deep Perimeter undercutting removes weight from the entire area behind the face area to create the largest undercut possible resulting in the largest free floating face Cobra has ever created Harmonic Cavity Insert: An Engineered Thermoplastic Urethane vibration damping insert is positioned directly behind the impact zone The Loft and CG of each iron is tuned to deliver the optimum trajectory and distance gaps