i dont actually know what its called but i was replacing my rear cv and was having some some trouble getting the outside to come off and ended up hitting that shaft that runs through the drum assembly with a hammer to see if it would help. it didnt. i got it off and the new axle installed but now that shaft is wobbly. tightened down the castle nut and still is really loose. so if anybody know what that shaft is actually called so i can order a new one or if you have any suggestions for me it would be appreciated 

The axle nut requires some 145 lb torque as it is not a spindle bearing. The flat washer is a spring washer and should be installed with the convex side towards the nut tot hold torque.

 

IF 145 lb doesnt draw the shaft through or hold the wheel tight, the bearing likely has failed (busted cage)

Sounds like the bearing is shot. What year's your ride?