Matte black finish: The Roller plastic knob has a durable matte black coating. This surface will not wear down over time and provides sufficient texture for grip. Galvanized steel: The bolts and washers of the walker accessories are made of galvanized steel. When you go out, they can withstand humidity and weather conditions. Anti slip: Roller accessories will not slip. This helps to make the walker sturdy, durable, and safe to use. Easy to use: Driver assistance accessories require simple assembly. It only takes a few minutes to connect. Scope of application: The transmission drum accessory package includes 2 plastic knobs and 2 bolts with washers. Bolt size: M6 * 35mm These can be easily assembled by hand. When shopping, please pay attention to the size and dimensions of the product to ensure it meets your needs. In the title and, we provide detailed information about the product, including its features and specifications. We hope you are completely satisfied with your purchase, so please feel free to contact us if you have any questions or concerns. We are always available to assist you and will do our best to provide assistance to you. Thank you for choosing our product. We hope you like it!