Because the bolt-on axle bracket that comes with a Ridetech 4-link bolts to the factory leaf spring bracket, which is welded to the stock axle from the factory, Ridetech has developed a weld-on bracket that can be welded directly onto an aftermarket axle. If you are using an aftermarket axle, this is a much simpler way to install a Ridetech 4-Link. Sold Individually.