Grinding wheels are either made of gray corundum (carborundum) and ceramics binder (bench grinders) or of high quality white corundum and glazed ceramics binder (sharpening machines).
Grinding wheels are available in different grits: the higher the number the finer the grit (suitable for deburring and finishing), whereas the lower the number the rougher the grit (suitable for grinding and roughing-out).