Masterbuilt Premium Phosphor Bronze 13-56 Acoustic Guitar Strings for authentic acoustic guitar tone, projection, and performance. Masterbuilt Premium Phosphor Bronze acoustic guitar strings come standard on Gibson Montana acoustic flat top guitars. They bring out the natural and expressive tone of a flat top. Masterbuilt guitar strings are manufactured under the direction of Gibson's acoustic luthiers, and are round wound with phosphor bronze wrap wire, to give you a bright attack and sustained warmth. Ideal for acoustic flat top guitars, they bring out the natural expressive of acoustic guitars. The best guitars deserve the highest quality strings, and Gibson takes every extra step to ensure that Masterbuilt Premium strings are the world's finest acoustic guitar strings. It's more than using top-grade materials. It's manufacturing under tight quality control standards, as well. This guarantees the perfect match between instrument and string will yield the true measure of quality - tone, durability, and consistency. String Diameters: .013 .017 .026w .035w .045w .056w inches (w = wound) Medium Gage Note: Image shown is a 12-53 set, for example only. Vacuum packed to ensure maximum life. Available for Order