My truck is full of those, can you be more specific?

I'm most concerned about the bearings in the 9 inch. Tomorrow I'm going to replace the pinion seal, but I am concerned about all the bearings inside the axle. Also, since I'll be changing the fluid, I'll have the chunk out and can "inspect" it for damage. Only problem is I have no idea what I'm looking for. Can someone link me to some videos/pics/anything useful?