All D'Addario Pro-Arte treble strings are measured by a sophisticated computer controlled laser which performs consistency and quality checks, insuring true sounding trebles in every set. Basses are made from Silverplated Copper wound on Nylon. D'Addario is the world's largest manufacturer of strings for musical instruments. Many top guitarists won't play any other brand. Regardless of your playing style, D'Addario has a set of strings that's right for your classical guitar. Gauges 28-32-41-30-36-44.