STX Sync Series 2 Putter The STX Sync Series 2 Putter is a beautifully designed mallet that will utilize the latest STX insert development known as F.E.E.L. technology. in.F.E.E.L in.. is short for Friction Enhancing Elastomer Layer and it dramatically increases the coefficient of friction to put a greater amount of topspin on the ball and keep your putts on line. The soft face keeps the ball in contact with the putter longer for control while the in.bullet back in. style with unique heel and toe design elements increase the moment of intertia. Additional Features: Putter Type: Mallet