This is GNP's Rear Differential Carrier Bushing.
Have you ever heard that " thump " from the rear end while you are giving your Wrx or Sti the beans?
That's the sound of the rear differential hitting against the chassis of the car. Not good! And no wonder, if you have ever had the stock bushing in you hand, it's a joke! Soft rubber, with voids in it.
GNP's rear diff bushings are available in race or street versions, they're made from solid polyurethane that doesn't allow the rear diff to move anywhere near as much as it used to with the old stock bushings. Giving you a more direct transfer of power to the wheels.
Without the hard thump from the rear end, during gear changes.
FITS ONLY: 2002 - 2007 Impreza
2002 - 2007 WRX
2004 - 2007 STI
2004 - 2008 Forester