There really is no need to buy a special diff sanding tool. An old diff hub (or even the one off your current car) works just the same. One word of caution though....if you do use your current diff hub to hold the diff ring while rubbing it on emory paper.......be sure to remove the bearing(s) first. You surely won't want to take a chance of getting any of the grit from the sanding operation into the bearings.