Extreme Notch Weighting and the deeper 360-degree Undercut Channel increase the MOI by a substantial 8%. More weight has been repositioned away from the center and toward the heel and toe areas, so you get greater stability and forgiveness along with less distance loss of off-center hits. Constant-width sole reduces digging on hat, heavy or chunked shots. Sets now come 4-9, PW and Gap Wedge. The Callaway Big Bertha irons set has uniflex steel shafts.