CO-600-MB Corelli Solea violin string set 4/4 medium CO-680-M Corelli Solea cello string set 4/4 CO-682-M Corelli Solea cello string D-2 4/4 CO-683-M Corelli Solea cello string G-3 4/4 CO-684-M Corelli Solea cello string C-4 4/4