EJ44, extra hard tension, is optimal for maximum string resistance and projection without compromising tone. Pro-Arte, the world's most popular classical strings are D'Addario's premium classical guitar string sets. 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. Extra hard tension for maximum volume and resistance Laser sorted clear nylon treble strings for consistent, precise intonation Precision wound silver-plated basses for warm, projecting tone and the utmost consistency Made in the U.S.A. for the highest quality and performance String Gauges: Trebles .0290, .0333, .0416 Basses .030, .036, .045