Lippert 279687 Equa-Flex Suspension Upgrade Kit for Tandem Axle 4K - 6K Equa-Flex rubberized equalizers replace standard cast equalizers to provide a more comfortable towing experience by absorbing road shock/vibrations and reducing fore to after trailer movement knows as 'chucking' 4,000-6,000-pound Axle Capacity Tandem Axle Configuration Easy bolt-on installation; Trailair by Lippert Components Equa-Flex Suspension Upgrade Mounting hardware included