400-Grit sanding discs are an ultra-fine grit sandpaper for sanding between coats of stain or sealer. For smoothing of the surface, removing smaller imperfections, and removing marks. Its tempting to buy coarse 60 or 80-grit paper to speed up the sanding job. However, because modern lightweight joint compound is so soft, heavier grit sandpaper is not a necessity. Coarse-grit paper may have a tendency to leave undesirable sanding marks. We recommend 120-grit, 150-grit paper or higher for the best results.