Martin Acoustic Strings - light (12-54) - 3pkAuthentic Acoustic SP Guitar Strings Phosphor Bronze Martin Authentic Acoustic Superior Performance SP strings feature higher tensile strength and tin plated core wire on all six strings that enable a fuller and more balanced tone, quicker response and increased tuning stability. Our impeccable standards for acoustic guitar tone are embedded in our string design and precision manufacturing process. Features: Higher Tensile Strength Tin Plated Core