Born from D'Addario's greatest breakthrough in string innovation, XS Phosphor Bronze strings have the longest life of any D’Addario mandolin string. The XS coating gives warm, balanced phosphor bronze strings maximum life, with an uncommonly smooth feel. Made with a NY Steel core, phosphor bronze wrap wire and Fusion Twist technology, XS coated mandolin strings have incomparable break strength and tuning stability, in addition to their dramatically increased lifespan. 11-40 Custom Medium gauge strings provide more volume and resonance than Light strings, while still maintaining playability.