A "grater blade" refers to a sharp tool with small holes used for grating or shredding food items, like cheese or vegetables, into small pieces or thin strips. Full definition
Using the large grater blade on your food processor, grate the vegetables and place into a colander. (joannafrankham.com)
First you need to grate the carrots but for that you can use your food processor with the fine grater blade to make the process easy and quick. (flavorquotient.com)
I used the smallest grater blade because that's the only one I've ever used. (healthylivinghowto.com)