Made in 2007. Using the Progressive Wall Reduction System, Callaway Golf engineers lowered the center of gravity (CG) 6 percent more than in the X-18 Irons. Progressive Wall Reduction means the CG gets progressively lower throughout the set. The CG is lowest in the long irons, helping you get the ball airborne more easily. With its traditional styling and Callaway Golf core technologies, the X-20 Irons provide the performance and forgiveness to play the game with enhanced confidence.