In normal, straight-ahead driving, the drive shaft turns the drive pinion, which turns the ring gear. The ring gear turns the entire differential case because it is bolted solidly to the case . Since the pinion shaft is bolted to the case, it revolves with the case. The differential pinions also turn end-over-end with the pinion shaft. The differential pinions press against the side gears, and the side gears rotate. Since the axle shafts are splined to the side gears the shafts also rotate.