Quality Material: Crafted from steel, this product offers exceptional wear resistance and protection, making it ideal for daily use and outdoor conditions. It extends the lifespan of your child's bike, reducing the need for frequent replacements Precision Anti Friction Design: The 9 pieces set and ball bearing assembly are precisely engineered to minimize friction during axle rotation. This ensures smoother pedaling, efficient power transfer, and helps children easily master cycling skills Easy Installation Experience: Designed with user friendliness in mind, the installation process is straightforward to follow. Parents can quickly complete the setup without needing specially tools or skills, saving both time and effort Wide Compatibility for Models: Highly versatile, this product is compatible for most 12 inch - 20 inch children's bicycles and some tricycles on the market. There's no need to worry about model compatibility issues when upgrading your child's bike performance Stable Riding Assurance: The integrated design of the bowl set enhances axle stability in children's bikes, minimizing wobbling during rides and providing a safe and smooth cycling experience for kids Specification: Material: Steel Size Chart: Suitable for 12-20 inch Kids Bicycle Package Includes: 9pcs/set Bottom Bracket Cups Note: Please allow slightly errors 1-2cm/0.39-0.79inch differences due to manual measurement.