Grit

Grit is the abrasive particle size rating printed on sandpaper and sanding discs, based on how many particles fit through a standardized screen per square inch -- counterintuitively, a lower number (like 60) means larger, coarser particles that cut fast and aggressively, while a higher number (like 320) means finer particles that smooth and polish. Sanding is almost always done as a progression through increasing grits, each step removing the scratch pattern left by the one before it.