They are "full floating" meaning that the bearings ride on a spindle and the housing carries the full weight, where the stock housing on Toyotas the housing and the shaft share the load making it more vulnerable to shaft breakage. It's kind of a "I am cooler than you" upgrade not really necessary but will add a great deal of strength to your rear end and still be all Toyota. Check Pirate for a couple of build ups on these axles.
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