[onewhippedpuppy]

The factory aero kits on the 986/996 have clips with a threaded hole that attaches to the pinch weld on the underside of the body, the screws that attach the bottom of the skirts screw into these clips. The upper portion of the skirt is held on with 3M (or similar) double sided trim adhesive tape, you can buy it at most auto parts stores. The upper portion also rests on an aluminum ledge that screws to the body. There is typically one screw front and back where the skirt wraps around into the wheel well.

For the 996 these clips are 999 507 640 09 and listed as a u-clamp. I couldn't find them in the 986 parts catalog but they should be the same.