(EJ29) D’Addario Classic Silver-Plated Wound, Rectified Clear Nylon, Moderate Gauges: .027 .031 .039 .028 .033 .042 The original D'Addario classical strings. Each ‘rectified’ treble string is precision-ground using a proprietary centerless grinding technique. Roundness & dimension control are unsurpassed, ensuring absolutely perfect intonation. Rectified trebles are preferred by many recording artists for their distinctive warm tone and lightly textured feel. All Classics bass strings are silver-plated copper wound.