The 243 achieves its distance capabilities through two crucial pieces of technology. First, the irons are crafted from exceptionally durable 4120 Chromoly, allowing for a thinner, faster face. While this may seem like a simple solution, Grain Flow Forging this advanced material to exacting specifications and strength requirements is a technique requiring Mizuno's unparalleled skill and near century's worth of experience. Second, a Flow Microslot carved behind the face creates increased flexion at impact, producing a spring-like, speed-inducing effect. The slot progresses in size throughout the set with the long irons receiving the most distance aid.