On the sti bumper there is 3 small slots that the top of the winglet clips into. If you are fitting them to a wrx, cut the tabs off the top of the winglets and stick on with tigerseal or any windscreen glue, thats what i did to my wagon.
Got followed all the way from royston to stevenage in my GTR on the baldock bypass a few years ago by a green unmarked ford mondeo, i was going a little bit fast