Ernie Ball 2002 Earthwood Medium Acoustic Guitar Strings 13-56 2 Pack Medium Gauges: .013, .017, .026, .036, .046, .056 When you open a pack of his strings today, you know you're getting a quality set of strings designed to give you great tone, reliable performance, and long life. Made from 80% copper, 20% zinc wire wrapped around hex shaped tin plated steel core wire. The most popular acoustic guitar strings provide a crisp, ringing sound with pleasing overtones.