Martin Find Your Acoustic Guitar Strings - Medium Gauge VarietyMedium Gauge Variety Includes: Martin MA150T 13 56 Medium 80 20 Bronze Treated Acoustic Guitar Strings 41Y18MA150T Martin MA150S Authentic Acoustic Marquis Silked 80 20 Medium 13 56 Acoustic Guitar Strings MA150S Martin MA550 Medium 13 56 Phosphor Bronze Acoustic Guitar Strings MA550 Martin MA550T Treated, 13 56 Medium, 92 8 Bronze Acoustic Guitar Strings MA550T Martin MEC13 Eric Clapton's Choice Medium Phosphor Bronze Acoustic Guitar Strings MEC13