Callaway X-18. The best-selling Callaway X-Series irons feature the patented core technologies that have made the Callaway Golf the most innovative iron manufacturer in the world. Extreme Notch Weighting, a proprietary visible feature that raises each iron's Moment of Inertia for increased stability and better results on off-centre shot, combines with a deeper 360-degree Undercut Channel to achieve even more increased forgiveness. The S2H2 (Short Straight Hollow Hosel), a staple of Callaway Golf irons for more than 15 years, allows weight to be moved lower and to the more useful perimeter area of the clubhead. An integral element of the S2H2 design is Tru-Bore Technology, which extends the shaft tip completely through the clubhead to the sole for greater feel and superior control. VFT (Variable Face Thickness) face design technology allows Callaway Golf to raise or lower the centre of gravity for optimum trajectory with each iron in the set: resulting in a higher launch angle in the long irons and better trajectory height control in the short irons and wedges. Callaway X-18 irons feature a standard progressive offset throughout the set and fully balanced sole engineered to improve turf interaction and workability. Standard X-18 irons are available in 2-iron through 9-iron plus Pitch (46 degrees), Approach (51 degrees), Sand (56 degrees) and Lob (60 degrees) wedges. The standard steel shaft is the Constant Weight Uniflex by True Temper. Graphite shaft options are System 55i (light flex), System 75i (regular flex), System 85i (stiff flex), and Gems(TM) 45i (ladies flex).