D'Addario XT16/56 Phosphor Bronze Medium Coated Resophonic Guitar StringsNever Fade Away D'Addario XT Strings last 4 times longer than traditional uncoated strings without sacrificing the tone or feel that players know and love. Extended Life Natural Feel Since D'Addario introduced Phosphor Bronze strings in 1974, they've been synonymous with warm, well balanced tone. XT Phosphor Bronze resophonic guitar strings offer that and more, boasting enhanced break resistance, better pitch stability, and longer life than standard