The reason for the two nuts is one is a locking nut. The "inner" nut is for adjusting the wheel bearing tightness. The "outer" nut is to lock it in place. Rotate the drum/hub when seating in new bearings. It will save you from having to do the job again soon. Also, there should be a locking ring inside the hub, which you can use a dentist pick or hook style tool to remove
