EPS530 s offer a super-bright crunchy tone and corrosion resistance for longer string life. D Addario XL prosteels utilize a highly magnetic corrosion-resistant steel alloy that delivers super-bright tone without shrill overtones. They offer a palette of harmonically rich brilliantly penetrating highs combined with pronounced tight-and-tough lows. If you re looking for more crunch bite and sustain ProSteels are the choice for you. Made in the USA D Addario electric guitar strings are made in the USA drawn to our exacting specifications at our New York production facility.