For the 2002-2007 WRX, we offer 2 short shifter options: The Wide Barrel option and the Narrow Barrel option. The Narrow Barrel option is for cars that came from Subaru with the factory short-shift option. The Wide Barrel option is for all other applications. To determine if you have the factory short-shift option, you will need to remove your shifter cover and measure the width of the shifter where it connects to the fork.
If the shifter fork width is 1.155" (inches), you will need the Narrow Barrel.
If the shifter fork width is 1.435" (inches), you will need the Wide Barrel.