The grinding disc is flat with a plastic back. The sanding disc fits most angle grinders and does not require a backing pad. The grinding disc attaches directly to the hand of the grinding machine. In comparison to depressed center wheels or resin fiber discs it is lighter, cuts faster, and grinds faster while leaving an even surface. Plastic Backing Disc have advantages , it is not easy to break and deform when damped,it uses special high quality engineering plastic as the backing,which increases the strength of product. The Disc can be dry grinding as well as water polishing,water resistance is good,not easy to deform. Plastic backing disc design allows for more control when grinding corners and edges. No deformation when used in heat or humidity . Can be Used both wet and dry. No back-up pad needed.