Ernie Ball Earthwood 80/20 Bronze Acoustic Guitar Strings are made from 80% copper, 20% zinc wire wrapped around hex shaped brass plated steel core wire. These acoustic guitar strings provide a crisp, ringing sound with pleasing overtones. Gauges .009 .009, .012 .012, .020w .009, .026 .012, .036 .020p, .046 .026.