Introducing Nickel Chromoly – A new material with so much additional ball speed, our engineers switched their focus to feel and stopping power. At 35% stronger than our original Hot Metal material, 4335 Nickel Chromoly enables a high-energy 8% thinner clubface. Combined with Mizuno's vibration controlling V-Chassis and deep CG design, the JPX923 Hot Metal irons are as enjoyable and controllable as they are long. The Pro model is more compact, with minimal offset for confident ball-strikers seeking maximum ball speed.