Designed to cope with demanding practices and schedules. Martin Authentic Acoustic SP Phosphor Bronze strings feature their highest tensile-strength core wire and are tin-plated for enhanced corrosion resistance. These Acoustic SP strings provide players with good tuning stability as well as a true and consistent tone throughout gigs. Manufactured with copper tin and phosphorous Phosphor Bronze strings yield a dark and slightly warmer tone that 80/20 strings. These Acoustic SP strings include gauge 13-17-26-35-45-56. Features Set of 6 acoustic guitar strings Medium gauge 13-56 Metal wrap wire composition of copper tin and phosphorous Tin plating offers added corrosion resistance Specifications Gauges: 13-17-26-35-45-56 Tension: 190.9