This is a replacement part that uses our Black Series material to boost stiffness over the original part by 18% to withstand increased loading seen by this position on the car. PFF5-4001GBLK provides a fixed 5mm offset to provide +/- 0. 5 caster offset for improved steering feel. Additional caster will also create additional negative camber on turn giving improved tyre contact with the road under heavy cornering. For a non-adjustable version of this bush por favor use PFF5-4001BLK.