This is a set of Authentic Acoustic Lifespan 2.0 phosphor bronze strings from Martin. Lifespan 2.0 strings are engineered using a new patented technology developed by Martin to protect the core and wrap wires to prevent corrosion without compromising your tone. Authentic Acoustic Lifespan 2.0 strings look better, sound better, and feel better, providing a smooth playing experience that reduces finger drag. These are Marquis Silked strings with wrapped end windings to protect the bridge of your high-end instrument.Medium: 13-17-26-35-45-56