Material: The whole is made of high-grade metal, after special processing, corrosion resistance, good heat resistance and long service life. Purpose: Internal thread work well, which can ensure the close connection with the bicycle hub and stable rotation. Applicability: Easy to operate, low noise, suitable for mountain bikes, folding bikes and other common bicycles on the market. Important note If you have any questions, please feel free to contact us, we will provide you with quality services and caring answers. safety:Using high‑strength steel, it has good corrosion resistance and heat resistance Specification: Item Type: Freewheel Cassette Material: Steel Product Weight: Approx. 619g / 21.8oz Level: 9 speed Gear Ratio: 11-40T (11-13-16-20-24-28-34-40T) Type: Super Fluid Drive positioning type Package List: 1 x Flywheel 2 x Sprocket 1 x Flywheel Cover Note: After the installation is complete, check whether the flywheel is locked and whether it is aligned.