SET OF STRINGS FOR CLASSIC GUITAR WELT '' Gold Alloy '', raw in transparent nylon. Strong Tension. The Pro-Arte strings are our sales leader in the whole world and the best D'Addario strings for Spanish guitar. All Pro-Arte strings are classified by a highly sophisticated computer controlled laser machine that performs diameter / tension measurements and quality control, ensuring great sound and precise treble in each game. Pro-Arte bass strings are wound using a silver-plated copper over a multi-filamented nylon core for a warmer and more projected shade.