EPS510's offer a super-bright, crunchy tone and corrosion resistance for longer string life. D'Addario XL ProSteels utilize an exclusive 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. Regular Light gauge. Exclusive corrosion resistant steel alloy offers brighter, crunchier tone and increased sustain. Environmentally friendly, corrosion resistant packaging for strings that are always fresh. String Gauges: Plain Steel .010, .013, .017, ProSteels Wound .026, .036, .046.