Thomastik-Infeld Spirocore 3/4 Upright Double Bass A String - Medium Gauge - Chromesteel Wound Flexible Spiral Steel Core A String For Upright String Double Bass Medium Gauge Chromesteel Wound Flexible Spiral Steel Core 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.