Suitable for 5-speed 6-speed and 7-speed models to meet the needs of different users. Using good-quality materials and accuracy craftsmanships to ensures a smooth shifting , improving cycling efficiency and comfortable. After special ,excellent wear resistance and resistance, extending its service life and reducing maintenance costs. On the premise of ensuring strength, try to reduce of the flywheels itself as much as possible and improve the flexibility of the entire vehicle. The structure is reasonable, ensuring smooth gear shifting and avoiding chain breakage or lagging, providing a better cycling .