Crafted on the foundation of hexagon tin plated steel core wire with a wrapping wire consisting of 80% copper and 20% tin, the Ernie Ball 2003 Earthwood Medium-Light 80/20 Bronze Acoustic Guitar Strings are an industry standard for a well-fitted acoustic. Easier and lighter to play thanks to the .012 through .054 gauge size, this pack is a favorite for easy strumming or those building their callouses.