Martin Acoustic MA540 SP Phosphor Bronze Light 12-54 Guitar Strings, 3 PacksValue 3 Pack 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. Gauge: Light E: . 012 B: . 016 G: . 025 D: . 032 A: . 042 E: . 054 Tension: 168. 5