The DAC series represents the most widely used first-generation hub bearing unit, featuring a double-row angular contact ball design arranged back-to-back (DB). These bearings utilize integrated inner and outer rings and incorporate double-sided rubber seals; they are pre-filled with specialized grease and have preset axial clearance at the factory, requiring no adjustment upon installation. Utilizing steel balls as rolling elements—which maintain point contact with the raceways—the series achieves a friction coefficient of only 0.001–0.002.