7 sizes for broad compatibility Includes 7 bearing sizes to fit various bike models Size range from 4032 mm down to 21 mm Suitable for MTB, road bikes, children's bikes, and common bottom brackets Clear specifications you can rely on Outer and inner diameters range from 32 mm to 40 mm Steel ball diameter varies from 4 mm to 8 mm Made from steel for durability and long life Easy installation and upgrade Package includes 2 bearings Simple replacement or upgrade for your headset or bottom bracket Remove the old bearings and insert the ones to restore performance Smooth performance you can feel Precise steel balls enable smooth, lowfriction movement Improves overall headset and bottom bracket operation for a better ride Practical use scenarios Replacing worn bearings on a mountain bike headset to restore steering feel Upgrading bottom bracket bearings on a road bike to improve pedaling efficiency Maintaining a child's bike to ensure safe, smooth rotation and reliable operation Compatibility and reliability Works with a wide range of bike types and common bottom brackets on the market Designed to provide durable, longlasting performance with regular use