This SES suspension upgrade fits the trailer suspension with an underslung axle setup that has a 2-3/8 in. up to 3 in. diameter axle with 2 in. wide leaf springs. Each laser cut piece of steel is precision bent and powder-coated to ensure a quality fit. The hollow rubber springs are designed to deliver a progressive spring rate. In other words, the more weight that pushes down on the rubber springs the harder they work to prevent sag and stabilize the load. This kit is rated at 5,000 lbs. capacity. Even though you're increasing the spring rate by adding this upgrade, this does not increase the trailer's GTW. Please make sure that the load does not exceed the GTW (Gross Trailer Weight) set by the manufacturer.