Aquila 143U Tenor set Key of C - GCEA High G. Aquila's Carbonblack Ukulele Strings Set give you a unique musical feeling and a strong, consistent sound, far better than Fluorocarbon. Carbonblack is Aquila’s answer to Fluorocarbon strings, which are bright but at the same time may sound static and lifeless, without emotion. The musical results with Carbonblack strings are really amazing: a more brilliant sound than fluorocarbon, they are more powerful and more emotionally responsive through the entire range of the fretboard. Carbonblack, compared to other strings, also gives the instrument more precise intonation and better tuning stability.