Callaway Golf Men's XR Pro Irons Set (Set of 7 Total Clubs: 4-PW, Left Hand, Steel, Regular Flex) Revolutionary Ball Speed From Cup 360 Our improved face cup technology even acts like a spring on shots hit low on the face to increase ball speeds; The speed is higher at every other impact location on the face too Lower CG, More MOI and Ball Speed The Internal Standing Wave is the ultimate team player; It's refined the way that we lower CG, increased MOI and gives the face cup the freedom to flex for more ball speed New Construction And Refined Shaping A player's iron needs a different level of refinement and attention, in this case a 2-piece construction that includes a dual heat treatment The head shape is more compact, with a thinner topline and narrower sole width