LOOSE STRING FOR DOUBLE BASS Helicore Hybrid '', Re (D), HH 612 3/4 medium tension. Helicore Orchestral Strings for Double Bass are made with a core made up of various braided steel threads, producing a warm and moderate tonal quality. The heart design makes the strings very easy to play under the left hand. The string damping has been optimized to create a good balance between sustain in pizzicatos and altocar response with the bow, giving us great response in many different styles, from a symphonic style to jazz or bluegrass.