Callaway Golf Men's X Series N15 Irons Set Deep Undercut Cavity: This cavity allows the face to flex and rebound at a higher rate increasing the ballspeed resulting in consistently longer iron shots Perimeter Weighting: Lower sweet spot, higher launch angles and more forgiveness are all the result of the perimeter weighting in these irons A Deep Undercut Cavity located behind the face of these irons combined with perimeter weighting moves the sweet spot lower in the clubhead resulting in faster ballspeeds