Extension Bar Set is used with the Snap-Loc Dolly System to extend the height of our Push Bars or Panel Bars and can be used to transform two Push Bars into a Panel Bar Set! The Snap-Loc Dolly System is the easiest, fastest and safest way to move more in less time! THE PROBLEM: Cheap dollies have junky casters that don't roll well, break often causing valuable items to dangerously fall and waste your time and money. THE SOLUTION: The Snap-Loc Dolly has high capacity smooth rolling casters, is USA made to last a lifetime, offers E-Track Strap cargo anchoring with Push-Panel Bars that transform to move everything with ease! You're going to love it! Dolly System also coordinates with the Snap-Loc E-Track Single System to secure cargo and items on pickups, trucks, trailers, racks, walls, floors, ceilings and more!