Corelli CO-304-B double bass string E-4 1/4, 90 cm., rope core, nickelCorelli CO 304 B double bass string E 4 1 4, 90 cm., rope core, nickel Corelli's Nickel Soliste Series and Nickel Orchestre strings combine tradition and innovation. They present the same high acoustic qualities and benefit from the same innovations as the Tungstne Series 370 and 360. As a result they offer real advantages in comparison with other existing traditional strings.