Corelli Double bass strings Solo tuning nickel - Extra strong (391TX)4 4 and 3 4 size. The 390 series offers nickel strings in solo tuning. Traditional construction for a familiar playing feel. Bow position and pressure ratios remain familiar, but working with the strings is easier, they give a pure sound with a very rich harmonic spectrum. This set is designed for basses from 106 cm to approx. 110 cm. A Nickel Solo