EJ17 is a medium Phosphor Bronze set that offers heavier gauges for increased volume and projection. The increased tension makes them ideal for drop or altered tunings as well. Since D'Addario introduced Phosphor Bronze guitar strings in 1974, they have been synonymous with warm and well-balanced acoustic tone.Pioneered in 1974 and still revered today, Phosphor Bronze has become synonymous with warm, well-balanced acoustic tone. D'Addario Phosphor Bronze strings are precision wound with corrosion-resistant phosphor bronze onto a carefully drawn, hexagonally shaped, high carbon steel core. The result is long-lasting, bright sounding tone with excellent intonation. String Winding Technology String winding equipment is designed and built by D'Addario's engineering team, guaranteeing a production range of 500,000 to 700,000 strings per day. Digitally-controlled string winding machines ensure productivity, accuracy, and consistency. Hex Core Construction Precision drawn hexagonal core was pioneered by D'Addario. This innovation allows the wrap wire to grip the core for superior dimensional stability, enhanced durability, and precise intonation.