They are held on by double sided tape along the top. You also have to drill a couple of holes in the stock bumper under the foglight area, and then inside the wheel well. I could show you pics of my yet to be installed front extensions if you would like.
I just took a couple pics for ya, wasn't able to get the instructions because they are about 7 pages long and my camera ran out of batteries. Here is the inisde view of the left extension, you can see the screw holes and the tape along the top edge. The last pic is of the hardware that is needed for the install of both extensions.