IRON SRIXON ZX5MK2 MDS1105 6I #5-P SMAIN FRAMEMainFrame is a variable thickness pattern of grooves, channels, and cavities carefully milled into the backside of ZX4 Mk II, ZX5 Mk II, and ZX Mk II Utility Iron faces that maximizes flex at impact. MainFrame not only boosts COR, it also repositions mass away from the face and into the toe and sole for a lower Center of Gravity. This creates more than just faster ball speed, but also more consistency and forgiveness, enhancing all aspects