Martin MSP6200-4PK SP Lifespan 80/20 Bronze Acoustic Guitar Strings, Medium, 13-56, 4 Pack Treated with Martin's Clear tone proprietary technology for a longer lifespan than regular strings Designed to repel the oils and dirt that can deaden strings 80/20 bronze provides a bright and vibrant tone. Gauge (medium): .013, .017, .026, .035, .045, .056 Includes: 4 Packs of Medium strings & ChromaCast 4 Pick Sampler