The grinding brush set includes 2 brass brushes of 175 mm and 225 mm, and 2 stainless steel brushes of 175 mm and 225 mm. Brass brushes are used for removing dirt from colored soft metals such as copper, brass, as well as for marble, stone, and for fine surface grinding that a steel brush would damage. The stainless steel brush is used for fine finishing and grinding work, on metal, wood, removing rust and paint. It does not leave unwanted iron traces on the processed material, unlike a regular steel brush.