Quality strings since 1956; Steel core, metal alloy or fiber winding; Warm, brilliant sound and durability; The “Classic” series standard strings; The A+D strings of the “Special” series are 0.01 mm thicker; The “Superior” strings are 0.02 mm thicker than “Special”; The “Silver Sound” G strings with flexible steel core and silver winding; D “Classic” chrome steel; string thickness/tension: soft 0.97mm/13.6kp/29.9lbs; medium 0.98mm/14.0kp/30.8lbs; forte 0.99mm/14.1kp/31.0lbs;