Yonex Poly Tour Pro 125 16L Tennis String One of Yonex's most popular strings on the ATP tour and used by the likes of Nick Kyrgios and Martina Hingis, Poly Tour Pro provides great durability in a slightly softer poly. Gauge: 16L Diameter: 1.25 mm Composition: Co-Polyester / Monofilament Length: 39 ft. / 12 m