Rbz speed pocket in the 4-iron through aw works with an advanced ultra-thin face design and improved inverted cone shape to promote consistently high ball speed and distance on center and off-center hits, especially low on the face. hollow head construction inspired by our metal woods (4- through 7-irons) with substantial top lines, broad soles, superior perimeter-weighting, ultra-low cg and an ultra-fast 455 stainless-steel face for effortless launch and excellent distance. visible tungsten weights in the toe pulls the cg into the exact center of the face to ensure that center-face impact delivers maximum ball speed and distance. fantastic feel promoted by a specially formulated polyurethane developed by 3m that fills the speed pocket, keeping debris out and which quiets vibration without significantly slowing/inhibiting the flex of the pocket.