Martin MA540 Authentic Acoustic Superior Performance 92/8 Phosphor Bronze Guitar Strings - .012-.054 Light (25-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. Tech Specs Guitar Type: Acoustic Guitar Number of Sets: 25 Number of Strings: 6 Coated: No Gauges:. 012, .