Adds new life to old springs and reduces body roll with simple bolt on installation; variable rate leaves do not affect ride when unloaded; mounting kit sold separetelyHigh quality spring steel leavesRaised height and spring rate can be varied depending on adjustment of outer upboltsThe is load pro four leaf stack helper spring with 3500 pounds level load capacity. It has mounting kit sold separately and is backed with a lifetime warranty. Adds a new life to old springs and reduces body roll with simple bolt on installation and variable rate leaves do not affect ride when unloaded.