BASS STRING SET D? Addario EXL170BT XL series Nickel Round Wound 4 string bass (045-060-080-107). The D'Addario Balanced Tension XL Electric Bass Kits are made up of mathematically optimized string gauge combinations, resulting in more control and comfort performance. Combined with the distinctive bright tone of the XL Nickel Wound strings, each set offers greater dynamic control and a more consistent feel between strings for strumming, balanced bendings, picking and other techniques.