Martin MA150T 13-56 Medium 80/20 Bronze Treated Acoustic Guitar StringsMARTIN AUTHENTIC ACOUSTIC LIFESPAN 2. 0 GUITAR STRINGS 80 20 BRONZE Next 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. Gauge: Medium E: . 013 B: . 017 G: . 026 D: . 035 A: . 045 E: . 056 Tension: 189. 6