Choosing the right sandpaper for bodywork is more specific than it sounds and getting it wrong wastes time and produces inferior results.

For blocking primer to final guide coat: 180 to 220 grit open-coat aluminum oxide on a hard block. The 'open coat' specification means the abrasive is spaced to prevent loading — loaded paper doesn't cut, it just pushes material around.

For between-coat sanding in a final finish system: 400 to 500 grit wet. The grit leaves scratches that the subsequent coat fills. Too coarse and the scratches show through. Too fine and the mechanical adhesion between coats is insufficient.

For surface preparation before adhesion (rust converter, seam sealer, filler): 80 grit provides enough mechanical profile. Any finer and you're not creating the surface texture that allows adhesion.