Tier One T1-Firewire Co-Polyester Tennis String Provides Maximum Ball Bite and Tension Stability Designed to provide ideal string performance for players 3.5-5.0 NTRP Available Gauges: 16 (1.30 mm), 17 (1.25 mm), 18 (1.20 mm) Available Lengths: 12.2 m / 40 ft sets, 200 m / 656 ft reels Available Colors: Red, Black