Hey, Flitzer, it's actually a combination of techniques, but each rivet is actually a combination of about 5 visible layers: 1 for lighting the actual rivet, 1 for shading the actual rivet, 1 for lighting the dent in the aircraft skin put in by the rivet, 1 for shading the same, and 1 for the weathering the aircraft skin around the rivet where dust could accumulate (this highlights the rivet, too). For these I mainly use the Bevel and Emboss layer style for the lighting and the Outer Glow layer style for the weathering.
Cheers,
Logan