Yeah, there is a smaller needle bearing assembly that with unlocked hubs, allows the hub assembly to rotate around the stationary stub axle. When the hubs are locked in, the hub assembly rotates in unison with the stub axle. A larger bearing is used when the hub assembly is locked in as the hub needs some bearing to rotate around and allow the 4 studs holding it to the knuckle to stay stationary. In other words, the stub axle receives power from the transfer case in 4wd hi and low, and in order to drive the front wheels, the hubs provide the mechanical lock between the wheels and the stub shaft. Unlocked, the stub shaft doesn't rotate, but the wheel assembly does, so the needle bearing you can see is being used. When the hubs are locked, a larger bearing is used (non servicable to my knowledge) as the stub shaft and the wheel assembly have the same angular velocity. Since the needle bearing is rotating at the same velocity as the stub shaft, the larger bearing is then used to allow the powered wheel to spin in relation to the otherwise non rotating 4 stud knuckle assembly...