Die grinders spin at high speeds often up to 25,000 RPM and can thus move a fair amount of stone quickly if you have a good burr in them. A simple die grinder is perhaps 5 inches long and 2 inches or so in diameter. Air comes in at one end and the burr is secured in the opposite end.
Abrasive grains constitute the central component of any grinding wheel, and the hardness and friability of the grinding materials will significantly affect the behavior of a given wheel. Hardness is measured in terms of a relative scale developed in 1812 by a .