This axel set up tool is used to install Speed SXS Dual-Plunge or Factory XX Axles. No more guessing. Since all vehicles are different, a measurement needs to be made from the center of the differential to the hub plate.
The Speed SXS set up tool is inserted in the diff, where the axle would be inserted. It will sit flush against the diff. You need to also remove your hub from the trailing arm. The tool sits flush against the Diff and Hub plate of the trailing arm, providing exact alignment every time.