Is the fixed cam the hub or?

I bought a 2000 xterra 4x4 the guy said the fixed cam came apart when he was doing the brakes is it as simple as just buying a auto hub? if it is I might convert to manual hubs.I just want to know if the fixed cam is part of the hub or something on the axle.

Here ya go, hope this helps.

http://i71.photobucket.com/albums/i152/racerxxl/Xterra/Locations/AutoHub.jpg