The grit size of the wheel determines the size of the abrasive particles on the grinding wheel. Grit is expressed in numbers, with lower numbers indicating coarser abrasives for fast grinding and material removal, while higher numbers indicate finer abrasives for smooth and detailed finishes. Selecting the correct grit is essential to achieve the desired result when sanding, cleaning or finishing. Coarser grits are ideal for removing old paint or rust, while finer grits are used for final smoothing and surface preparation for painting or other finishes.