Nike Pro Combo. This unique set combines the best of cavity back and bladed irons. Full cavity Long irons (3 & 4) Typically the hardest irons to hit. The low centre of gravity and high moment of inertia (resistance to twisting) make these long irons very easy to hit Muscle Cavity Mid irons (5, 6, 7) The muscle cavity design of the Nike Pro Combo irons combine forgiving heel-toe weighting with a shot shaping weight pad to maximise versatility. Blade Short irons (8, 9, PW). Short irons are all about feel and working the ball. Nothing accomplishes this better than a blade. The high centre of gravity prevents the ball from ballooning.