ACOUSTIC GUITAR STRING SET XTAPB1356 acoustic guitar string set with phosphor bronze alloy and XT coated anti-corrosion finish. Caliber 13-56. Its state-of-the-art coating ensures a 4 times longer life in the use of this rope without sacrificing the classic touch and sound that characterizes the D'addario rope. They have a carbon steel core NY reinforced for greater robustness and flexibility that improves tuning by up to 131%, in addition, they incorporate the Fusion Twist reinforced welded ball system that minimizes the risk of breakage.