D'Addario EJ45C Pro Arte Composites Normal Tension Pro-Arte Composite silverplated copper classical guitar strings provide longer life than traditional Pro-Arte strings. All Pro-Arte treble strings are sorted by a sophisticated computer-controlled laser machine which performs diameter/tension measurements and quality checks, insuring true sounding, precise trebles in every set. Composite sets feature an additional Composite 3rd string, which provides tonal options and nicely balances nylon and wound strings.