The standard offset Caster Adjustment Bushing replaces the big, squishy tennis ball that the front suspension pivots on with a harder polyurethane bushing. Despite the welcome increase in rigidity and decrease in movement, NVH changes very little.
 

Applied Models:

Impreza WRX 5-door: 2008+ [2.5-liter turbocharged]
Impreza WRX 4-door: 2008+ [2.5-liter turbocharged]

Impreza 2.5i 5-door: 2008+ [2.5-liter naturally aspirated]
Impreza 2.5i 4-door: 2008+ [2.5-liter naturally aspirated]

Impreza WRX STI 5-door: 2008-2010 [2.5-liter turbocharged]

Legacy sedan: 2005-2009 [all models]
Legacy wagon: 2005-2009 [all models]
Legacy Spec B: 2005-2009 [all models]

Legacy Outback: 2005-2009 [all models]

Legacy 3.0R: 2005-2009 [3.0-liter Flat Six]

Forester 2.5XT: 2009+ [2.5-liter turbocharged]
Forester 2.5X: 2009+ [2.5-liter naturally aspirated]