Experience in instrument making, string winding, and comprehensive sound testing make Martin M980 Nickel Wound Bluegrass Resonator Guitar Strings the best choice for your resonator guitar. All raw materials are of premium quality to assure brilliance, clarity, and longevity. Martin uses a nickel/steel alloy for tonal qualities which are best suited to accent the strong resonating tendencies. In addition, Martin Bluegrass resonator guitar strings are highly resistant to corrosion. Gauges 16-18-26-36-46-56.