1. High speed, . Because the bearings are , the speed and speed persistence time of each bearing begin to differ slightly, and it takes a period of running-in time to to one and a half minutes 2. Double-sided dust cover to reduce sand and dust ingress. The outer side adopts a sealed cover, the inner side adopts a nylon cage, the outside is sandproof and dustproof, and the inside is stable 3. Built-in 7 balls, stable and long-lasting speed. Unlike most roller skates on the market, there are 7 small balls inside 4. Carbon steel material, strong and . Suitable for a variety of products, such as roller skates, skateboards, etc Bearing name: black steel bearing Bearing bore diameter: 8MM Bearing outer diameter: 22MM Bearing thickness: 7MM Bearing specification: 608ZZ Scope of application: roller skates, skateboards, etc Note:the delivery does not contain lubricating oil Color:As Shown Material:Metal Package Contents: 16 * Bearings 1 * Box 1 * Tool Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.