1The flywheel rotates steadily without noise, ensuring a close connection with the bicycle hub and smooth operation. 2Made of highquality metal material, it has good corrosion resistance and heat resistance. 3There is no need to worry about longterm use of friction and heating, which will affect its service life. 4With a hollow design, the weight is reduced, and it will not add too much burden to your bicycle when using it. 5It has high strength, strong durability and abrasion resistance, compatible with 9speed mountain bike for HG system. Item Type: Freewheel Cassette Material: Chrome-Molybdenum Steel (nickel-plated surface treatment) Product Color: As Pictures ShownProduct Weight: Approx. 625g / 22.0oz Gear Ratio: 11-42T (11-13-16-20-24-28-32-36-42T) Compatibility: For 9-speed mountain bike for HG system 1 x Flywheel 2 x Sprocket 1 x Flywheel Cover After the installation is complete, check whether the flywheel is locked and whether it is aligned.