It is a splined shaft. The clip holds it in but stays on the axle when you pop it out. I've found the best way to remove the axle from the hub is to use an air chisel with a pointed bit. You have to disconnect the tie-rod end, endlink, and lower balljoint pinch bolt before doing this though. As for replacing the clip as well as the axle nut, I'm only gonna say I've had mine apart 3-4 times and have reused all the hardware with no problems. I'm gonna leave that up to you to decide though.
