Material: rubber and metal. High quality rubber and more stable bearings are wear-resistant, quiet and can work well with the case. Dimensions: 50 (outer diameter) x 18 (width) mm, center bearing inner diameter 6 mm, bearing inner diameter: 21mm. Equipped with 30mm and 36mm shafts and washers to meet different needs. Easy to install: The luggage compartment spare wheel is easy to pack and can be easily installed without a manual. Also pay attention to the tightening of the wheels during installation so that the luggage casters can roll better. Perfect solution: 4 luggage wheels, 8 axles, 8 axle bolts, 2 wrenches, 8 spacers Before ordering, please carefully measure the diameter and width of your old wheels to choose the correct size. When installing, pay attention to the tightness of the wheels so that the casters can roll better. Note: The data are all measured manually, please allow 1-3cm error due to difference in light and display, there may be some color differences, please refer to the actual item received.