Yonex BG66 Ultimax is a thin gauge (0.65mm) high intensity multifilament string offering the perfect balance of maximum speed, control and durability, making it the best choice for the worlds top players. Constructed with a high-intensity nylon core which gives 30% greater durability than normal nylon together with a high-polymer outer which provides sharp feeling and high repulsion - exceptional all-round performance from an extra fine string.