This is a special retainer to secure the jack screw found on John Deere number series tractors. Its purpose is to keep the jack screw from working loose from the wheel center hub. We make our retainers from mild steel and then zinc plate. The retainer is slid into a groove on the installed jack screw. A pair of pliers is then used to squeeze (crush) the retainer on the jack screw. This secures the jack screw until ready to use when separating the wheel wedge for wheel adjustment. We supply one on each of our Jack Screws we sell or as a 4pc kit.