D'Addario Helicore Cello Strings, Multi-Strand twisted steel core strings are superb for the advanced and professional players. The small string diameter provides quick bow response. Through special manufacturing techniques, the Helicore strings have a warm, clear sound with excellent pitch stability and longevity. Who is it for? Professionals, advanced students. Excellent for electric instruments using Piezo ™ pickups. Music Styles Classical, Modern Music, Jazz, Country.