Phosphor Bronze has been used for string manufacturing since 1974 and has since been known for its warm, brilliant, and balanced sound. D'Addario's Phosphor Bronze strings are made by winding corrosion-resistant Phosphor Bronze wire around a hexagonal carbon steel core. The result is a durable string with a strong tone and excellent intonation. Warm and well-balanced acoustic tone. Gauge: .013 .017 .026 .035 .045 .056.