Pro-Arte are D'Addario's premium classical guitar string sets and are the world's most popular classical guitar strings. All Pro-Arte treble strings are sorted by a sophisticated computer-controlled laser machine which performs diameter and tension measurements, ensuring true-sounding, precise trebles in every set. Pro-Arte basses are wound using silver-plated copper on a multi-filament nylon core for consistent and warm, yet projecting tone. The EJ49 normal tension set features black nylon trebles, preferred for their balance of rich tone and consistent intonation. Like all D'Addario strings, they come in environmentally friendly corrosion resistant packaging for consistently fresh strings, every set.