It basically sets your rear-end up like a ford 9". The outer bearings are pressed on to the axels, and there are retainers that hold the bearings into the axel tubes. The plate that the retainers bolt to is what gets welded on. This way if you break an axel, the bearing at the outer end is what holds the wheel and brake assembly in place, rather than the relatively tiny c-clip on the inner most part of the axel that will stay put while the rest of the axel/wheel and brake assembly exits the side of your car upon axel failure.
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Steve
72 Chevelle SS402/4sp