D'Addario EPS515 ProSteels Electric Guitar Strings, Medium, 11-50 Medium gauge Unique highly magnetic steel alloy offers brighter, crunchier tone and increased sustain Environmentally friendly, corrosion resistant packaging for strings that are always fresh Made in the U.S.A. for the highest quality and performance String Gauges: Plain Steel .011, .015, .019, ProSteels Wound .028, .037, .050