Matteo Berretini String of Choice. Firestorm is the string called our top of the Line String, Featured as X-treme Power, this is the string that is favorite amongst ATP Players using Signum Pro, this string has an amazing power, great durability, great tension mainteinance and a feeling that is worth trying. We´ve had amazing feedback from this string, so we think this is a must for any Tennis Enthusiast.
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