Tecnifibre X-one Biphase 16g Tennis String Natural - Reel [Misc.] Composition: composite microfilament biphase process and polyurethane Gauge: 16g (1.30Mm) 17g (1.24Mm). Length: 660'(200m) Durability: 16g- 6.76 17G- 6.3 Playability: 16g- 8.71 17G- 8.6 Misc.: Tecnifibre recommends pre-stretching this string.