Not sure what a "castin" is, unless you are fishing.

But the entire hub needs to come off of the spindle. Just like if you were repacking the front wheel bearings. there is a big nut behind a retaining washer in the end of the hub. Once the hub is off, you can get to the wheel studs.

If you are doing one, you might as well do all of the studs on that hub. It might save you some headache in the future.

Good Luck,
Michael