Phosphor Bronze has been used for string manufacturing since 1974 and has since represented a 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: .012 .016 .025 .035 .045 .056.