The top string on the pro tour gets a thin, 18 gauge (1.15mm) version for enhanced spin and power. Luxilon ALU Power Tennis String is used by roughly 60% of top 100 players because the poly-ether-ether composition offers consistent quality. The aluminum in the string improves playability by offering power and control for players with fast swing speeds. Each set of ALU Power is individually numbered for quality assurance and consistency set to set. Though the 1.15mm gauge is more spin friendly, it will not be as durable as the thicker 1.25, or 1.30 versions. Construction: Extruded Polyester Monofilament (Poly-Ether-Ether) Composition Color: Silver Gauge: 18 G / 1.15 Length: 40 ft / 12 m Features: -Best in class consistency and quality -Blend of power and control -Thinner gauge for more spin