Cognito 01-13 Chevy/GMC Silverado/Sierra 2500/3500 HD 2WD/4WD Torsion Bar KeysTorsion bar keys are used to set the ride height of the front of the truck and are commonly used in leveling kits, and it is important to set the height appropriately as to leave ample suspension droop travel to maintain a good ride quality. There are several different torsion bar spring rates that GM made and put in these trucks, the rate depending on the model and features of the truck. Some trucks that have a higher spring rate may not need