Martin Authentic Acoustic SP® strings offer excellent tuning stability, corrosion resistance and great playability. Engineered with the performer in mind, these strings are designed to stand up to rigorous practice and performance schedules. Martin starts with the highest tensile-strength core wire, then tin-plates it on all six strings for added corrosion resistance. When coupled with the highest quality wrap wire you get consistent true tone that you can count on song after song. Available in 80/20 Bronze and 92/8 Phosphor Bronze.