Optima 1747.M, String Set for Acoustic Guitars, Gauges: .013 - .017 - .026w - .036 - .045 - .057, Coating: 24-Carat gold-plated, E1 and B2 are made from high-quality nickel-plated steel wire and are additionally coated with real gold, Tinned steel cores for the G3 up to E6 strings, Gold-plated wrap, Roundwound, Made in Germany