This kit includes a Fuelab mini fuel pressure regulator, a Fuelab gauge for setting base pressure and checking fuel pressure as well as two -6 AN to 5/16th hose barb fittings to allow it to easily plumb in to your return fuel line and take the place of a stock regulator.  This kit is intended to be used on 2008+ WRX/STi applications but it can be make to work on older Subarus but you will need to run custom fuel lines.  There are several mounting options available and the regulator inlcudes a bracket which can be used directly or as a template to make your own bracket.  This FPR will usually cure the common GR STi fuel stumble and can help on the GR WRX as well when upgrading to bigger injectors.  In general, a higher quality regulator will smooth and control fuel pulses which takes care of stumbles and results in a much smoother running car.  Tuning is strongly suggested and it is important to set your base fuel pressure appropriately to either the stock base pressure (43.5 psi) or to the recommended base pressure for your application.