Ernie Ball Aluminium Bronze 13-56 strings. Made from a blend of copper and aluminum specifically tailored for acoustic guitar strings. Aluminum Bronze Acoustic Strings feature more projection and clarity than traditional bronze strings, while also providing improved corrosion resistance. Aluminum Bronze Acoustic Strings are made with Ernie Ball Maraging Steel hex cores and Aluminum Bronze wrap wire which provide more pronounced lows coupled with crisp brilliant highs. Medium Guages .013, .017, .026, .034, .046, .056