Callaway Golf X Hot Irons Set A combination of VFT and Hyperbolic Face Technology creates a larger sweet spot and increases ball speeds across the face for longer, more consistent distance Deep clubface/undercut cavity system enables engineers to precisely position the CG, increase face compliance and engineer the face of each individual iron to maximize ball speed Feel Management Technology; Produced through a dual material medallion that fine-tunes sound and promotes a crisp, dynamic feel at higher ball speeds Speed Step 85 Lightweight Steel Shaft; Steel shaft is available in both regular and stiff flexes along with lightweight graphite options