Flap discs are used primarily for grinding and blending. Surface conditioning flap discs are also available for deburring, cleaning, finishing, and polishing. Flap discs are three dimensional discs consisting of abrasive flaps glued to a backing plate of fiberglass, reinforced nylon, or metal. Interleaf flap discs alternate non-woven nylon flaps with cloth-backed coated flaps and are typically used for finer finishing and polishing work. Flap discs are available in two shapes, Type 27 and Type 29. Type 27 has a flat abrasive surface and is best for working flat surfaces or outside edges. Type 29 has an angled abrasive surface and is designed for aggressive stock removal. Common abrasive materials include alumina zirconia, ceramic, aluminum oxide, silicon carbide, and diamond. Choose from coarse to very fine abrasive grade, or corresponding grit, depending on material being worked and level of precision required.