Now in a convenient 3 pack Custom Medium gauge offers half gauges with a bigger sound and a bit more string tension. 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 produce a bright, balanced sound with pleasing overtones. Gauges: 13, 17, 26, 34, 46, 56.