Abrasives are tools for cleaning and shaping metal. sandpaper, grinding wheels, and sandblasting media are common shop examples. Mechanics use them to clean rust off brake rotors, polish valve seats, or prep metal for welding. The grit size determines how aggressive the tool is.
However, loose abrasives can ruin an engine. Grinding dust must be completely cleaned off parts before reassembly. If left behind, the grit mixes with oil and destroys bearing surfaces in minutes.