Developed under the direction of Gibson’s Master Luthiers, these strings are phosphor bronze wound to give your guitar a bright attack and sustained warmth, providing you with the ultimate acoustic sound. Suitable for any playing style, Gibson Phosphor Bronze strings are un-coated for an authentic acoustic feel, making these a favorite for the Gibson Team in Bozeman, Montana. Medium Gauge: .013 .017 .026 .035 .045 .056