The Martin MM12 Retro acoustic guitar strings represent yet another quality, vintage-inspired set of strings in Martin’s Retro line. These strings harken back to the 1930s, when nickel ruled the acoustic world. Made from Monel, a solid nickel/copper wrap, the MM12s let your acoustic’s natural wood tone ring through with a full low end, a high-end snap, and a solid midrange. The proprietary wrap on the MM12s is corrosion-resistant and impressively strong for a long life of uncompromised tone.