~ 1/2 inch. I saw a white piece of plastic with a bolt(?) sticking out to the left of the accelerator. It seemed to fit on it. The top of the unidentified piece can accept a Philips head screwdriver.
The carpet goes up onto the wheel well. To keep the carpet in place it is caught on a short threaded stud. The little plastic nut you found is supposed to be threaded on the stud to keep the carpet in place.
