STi stock bars? 06 WRX rear bar is 17mm. STi stock rear bar is 20mm (approx. 92% stiffer) Sway bars for the rear of the STI will not fit a WRX unless you swap the arms that the endlinks mount to, and pick up the endlinks. Otherwise, the STI bars line up directly over the top of the WRX style endlinks, and even if you can flex them into hooking up, you'll likely run into binding problems. If you're buying new or used, and want a 20mm bar, try picking one up from the 02-03 WRX sedans.
