Material: rubber and metal. Quality rubber and more stable bearings, wear, mute can work well with the case.Size: 40(outer diameter) x 18(wide)mm and center bearing inner diameter is 6mm,bearing inner diameter: 21mm. With 30mm and 36mm axles and washers to meet different needs.EASY INSTALLATION: Luggage compartment spare wheels are easy to pack, easy to install without manual. When installing, also pay attention to the tightness of the wheel, so that the luggage roller can roll better.Perfect Solution: 4 x Suitcase Wheels, 8 x Axles, 8 x Axle Bolts, 2 x Wrenches, 8 x Spacers Before ordering, please carefully measure the diameter and width of your old wheel to choose the correct size. When installing, pay attention to the tightness of the wheel so that the casters can roll better.When shopping, please pay attention to the size and dimensions of the product to ensure that it meets your needs. In the title and , we have provided detailed information about the product, including its features and specificationsWe want you to be completely satisfied with your purchase, so if you have any questions or concerns, please don''''''''t hesitate to contact us. We are here to help and will do our best to assist you.Thank you for choosing our product. We hope you enjoy it