Callaway Steelhead X-16 Pro Series. The Callaway Steelhead X-16 irons have a wider topline than the their predecessors - the Callaway X-14s. Featuring Callaway's patented VFT (Variable Thickness Technology) which enabled Callaway's designers to alter the thickness and raise or lower the centre of gravity for optimum trajectory with each iron in the set, the Steelhead X-16s also incorporate the Callaway 'Notch' weighting system which moves weight to the perimeter - the result is a club which not only plays easily - but looks like it plays easily. Utilising Callaway's 360-degree undercut channel which helps straighten off-centre shots, each iron has a low centre of gravity for getting the ball airborne quickly. A nice looking club with a soft satin finish. The Callaway Steelhead X-16 Pro Series is the low handicapper's version of the stadard model. These feature less offset - and a thinner topline and straighter leading edge than the standard Steelhead X-16s. While still very forgiving, the Callaway Steelhead X-16 Pro Series are suited to lower handicappers who like to shape the ball and prefer a more traditional feel to their clubs.