Hub bearings used to be more in pairs using single row tapered roller or ball bearings.With the development of technology,the car has been widely used car hub unit.The use range and usage of hub bearing unit is increasing day by day,and has been developed to the third generation:the first generation is composed of double-row angular contact bearings.The second generation on the outer raceway has a flange for fixing the bearing,which can be simply fixed by the bearing sleeve on the wheel shaft and the nut.It makes car maintenance easier.The third generation of hub bearing unit is the use of bearing unit and anti-lock brake system.The hub unit is designed with internal flange and external flange.The internal flange is fixed on the drive shaft with bolts,and the external flange installs the whole bearing together.