Pro-Arte strings are 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. • MFSKU J4305 • 019954234058