Thomastik-Infeld Spirocore 3/4 Upright Double Bass String Set - Medium Gauge Thomastik-Infeld Spirocore for Upright Double Bass are a flexible spiral steel core string that provide a quick response, consistent performance, with gut-like tonal power. This flexible steel core has greater elasticity than that of conventional strings, which means less inertia and a higher propensity to musical vibration. Full Upright Double Bass String Set Medium Gauge This Full Set Includes: Chromesteel Wound Flexible Spiral Steel Core G String, Chromesteel Wound Flexible Spiral Steel Core D String, Chromesteel Wound Flexible Spiral Steel Core A String, and Chromesteel Wound Flexible Spiral Steel Core E String