A new patented design for enhanced play and longer life. The Martin Lifespan 2.0 Phosphor Bronze strings feature new technology that protects the core and wrap wire to prevent corrosion. These Lifespan 2.0 strings include gauge 11-15-23-32-42-52. They were developed by Martin over a period of two years. This is to ensure that they look sound and feel better than ever before. Manufactured with copper tin and phosphorous Phosphor Bronze strings yield a dark and slightly warmer tone that 80/20 strings. Features Set of 6 acoustic guitar strings Custom light gauge 13-52 Metal wrap wire composition of copper tin and phosphorous Lifespan 2.0 strings have new patented design Look sound and feel better than Martins previous strings Provides smooth playing experience with reduced finger drag Specifications Gauges: 11-15-23-32-42-52 Tension: 155.1