D’Addario Mariachi Guitarrón strings feature Phosphor Bronze wound bass strings with NY Steel cores which provide better pitch stability and higher break strength The treble strings feature our monofilament nylon wrapped on monofilament nylon. Our proprietary loop end construction method ensures that these strings will fit any Guitarrón and will not prematurely break These sets are crafted with precision to perform and pay homage to the rich Mariachi musical culture Corrosion resistant packaging for strings that are always fresh. Made in the U.S.A. for the highest quality and performance