Ernie Ball ACOUSTIC Guitar Strings Bell Bronze Earthwood John Mayer Collab Medium 13-56 P02344Developed in collaboration with John Mayer, Ernie Ball Earthwood Bell Bronze acoustic guitar strings have been carefully crafted to meet Johns exacting standards, providing a new voice for your acoustic guitar. Inspired by alloys used traditionally for bells and cymbals, Ernie Balls patent pending Bell Bronze alloy offers a richer, fuller sound than any other string in our catalog. These strings will breathe new life into your guitar. Gauges: . 013, .