Martin Authentic Acoustic SP® strings offer excellent tuning stability, corrosion resistance and great playability. They are engineered with the performer in mind and they will always stand up to rigorous practice and performance schedules. Martin starts with the highest tensile-strength core wire, then tin-plates that core on all six strings for added corrosion resistance; because what you don’t see matters! Coupled with their highest quality wrap wire, you get consistent true tone that you can count on song after song. 80/20 Bronze - Bluegrass .012 .016 .025w .035w .045w .056w