This SES Suspension Upgrade fits the front suspension of a Ford F-650 & F-750 heavy duty conventional truck. Each laser cut piece of steel is precision bent and powder-coated to ensure a quality fit. Every hollow rubber spring delivers a progressive spring rate. In other words, the more weight that pushes down on the rubber springs (weight from a snowplow or heavy aftermarket accessories – such as a steel bumper) the harder they work to prevent front-end sag.