Pro-Arte strings are our the world's best selling and D'Addario's premium classical guitar 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. Pro-Arte basses are wound using silverplated copper on a multi-filament nylon core for consistent, warm-yet-projecting tone. Diameter Tension Item# Note inches mm lbs kg J4401 E 0.029 0.737 16.4 7.44 J4402 B 0.0333 0.846 12.5 5.67 J4403 G 0.0416 1.057 12.9 5.85 J4404 D 0.030 0.76 16.3 7.39 J4405 A 0.036 0.91 15.9 7.21 J4406 E 0.045 1.14 15.7 7.12