How are abrasives sized?
The size of the particles is important. Abrasive particles cut away the higher areas of a surface as they travel over it, but in doing so they leave behind scratches whose depth depends on the size of the particles. To remove these scratches, a smaller particle size must be used, and then a still smaller size to remove the scratches produced by the new particles, and so on until the scratches are so small they don’t matter. Many processes depend upon using progressively finer grits, from grinding a mirror for the Hubble Space Telescope to finishing furniture. Abrasives are, therefore, almost always sold by the size of the grit. An error amateurs often make in using products like sandpaper is using too fine a grade too soon, in the mistaken belief that this will produce a smoother end result. Starting with a grit much finer than the original surface imperfections will simply require more time sanding. So can skipping grades, depending on how long it takes to change grades. In changing g
