1 DOZEN FREE Callaway HX Golf Ball - Red ($30.00 Value) with Callaway X-18 Pro Series Iron Set Purchase! X-Series Irons from Callaway Golf have long been favored by some of the best players in the world because of their performance-enhancing technologies and by recreational golfers due to their forgiveness and great looks. The new X-18 and X-18 Pro Series Irons combine many of the same patented Callaway Golf core technologies used in earlier X-Series models with a new traditional head shape and size, and high-polish finish. The X-Series legacy of performance continues.