Jeff, Rob is talking about plastic "push-pin" type plugs. They look kinda like a mushroom with a flat head. The stem is 1/4" diameter with ridges that will hold them in place when you press them into the holes. The head is flat and about an inch in diameter.
Does that description help? If not, go find a new model Eddie Bauer and look at the fender flares. There will be gold ones holding the fender flares onto the inside of the wheelwell. You will see gold one inch plastic circular heads holding the flare to the body. Gofast suggested a generic store because they are cheap parts. You could get them from the Ford parts dept but they are a lot more expensive, and you'll need to buy about twenty of them.