This is Whiteline's adjustable rear swaybar for the 04+STi. Whiteline adjustable rear swaybars aid in reducing "roll" as well as helping with turn in and rotation of the car. Increasing rear swaybar size drastically changes the Impreza's handling balance for the better. These bars are three way adjustable with with one firmer and one softer setting. This allows you to fine tune the bar settings to your driving style as well as the other modifications you may make.