Callaway X-18 Pro Series Irons are the successor to the popular X-16 Pro Series Irons. Extreme Notch Weighting, a proprietary visible feature that raises each iron's Moment of Inertia (MOI) for increased stability and better results on off-center hits, combines with a deeper 360-degree Undercut Channel to achieve new heights of forgiveness. 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. Finally, VFT (Variable Face Thickness) face design technology allows Callaway Golf to raise or lower the center 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. The X-18 Pro Series Irons also feature a standard progressive offset throughout the set and fully balanced sole engineered to improve turf interaction and workability.