Callaway Big Bertha (2006 Series). Following on from the 2004 design, the Callaway Big Bertha 2006 Series irons embrace everything Callaway Golf stands for: Impressive performance through innovative technology. New weighting Technology strategically repositions clubhead mass towards critical heel and toe areas for enhanced stability and forgiveness, while reducing distance loss on off-centre hits. Proprietary Technologies including S2H2, Tru-Bore, Variable Face Thickness, and 360-degree undercut channel design vastly improve clubhead control, feel and efficiency. The improved constant-Width Sole Design decreases digging to eliminate fat shots and drives the club through a variety of challenging turf conditions. The High-Polish Finish is the end result of Callaway's innovative 17-4 cast stainless steel composition.