Specifications:8-speed hubs and 7-speed cards need to be equipped with washer or need to lengthen the bottom bracket.Meanwhile, it is very easy to use so it would be very convenient for you.Furthermore, due to its high quality material and fine workmanship, it comes with solid construction so it would be very secure for you to use.In summary, it would certainly be a perfect bike supply accessory for you to use.A washer needs to be added at the middle shaft:1. The chainring hits the frame.2. The crank hits the frame.3. The front gear cannot be moved down, the speed change is not smooth, etc.Washers are required at the hub:1. The flywheel is installed too loosely, and there is a crack.2. Such as 8-speed conversion to 7-speed flywheel.3. Modification of single-speed vehicles, etc.Item Name: Flywheel Hub WasherMaterial: Aluminum AlloyAttributes:Type A: Flywheel Hub Washer, 1.5mm BlackType B: Flywheel Hub Washer, 2mm BlackType C: Flywheel Hub Washer, 3mm BlackType D: Flywheel Hub Washer, 1mm BlackType E: Flywheel Hub Washer, 2.5mm BlackType F: Flywheel Hub Washer, 1mm RedType G: Flywheel Hub Washer, 1.5mm RedType H: Flywheel Hub Washer, 2mm RedFeatures: Stable, Durable, Easy to UseSize: Inner Diameter: 35mm/1.38", Outer Diameter: 40mm/1.57" (Approx.)Option Thickness: 1mm/0.04", 1.5mm/0.06", 2mm/0.08", 2.5mm/0.1", 3mm/0.12" (Approx.)Notes:Due to the light and screen setting difference, the item's color may be slightly different from the pictures.Please allow slight dimension difference due to different manual measurement.Package Includes:1 x Flywheel Hub Washer