Martin MA540TPK3 Authentic Lifespan 2.0 Treated Phosphor Bronze Guitar String Light 12-54 3 SetsNext generation Martin Authentic Acoustic Lifespan 2. 0 strings are engineered using a new, patented anti corrosion treatment only available from Martin. It protects the core and wrap wire to prevent corrosion without compromising tone or feel. Our impeccable standards for acoustic guitar tone are embedded in our string design and precision manufacturing process. Thats why we make our own. This is a 3 pack. Light Gauge 12 54