The shape of the flap disc, whether conical (Type 29) or flat (Type 27), provides different performance features. Smith & ARROW flap discs are Type 29. The flap disc generally have two shapes, which includes curved and flat. The flat type is also called T27 type, and the curved type generally refers to T29 type. Flat (T27) has smooth grinding surface and is mainly used to grind the plane and the outside corners. The angle between the flat flap disc and the grinding work-piece during work can be grinded and polished at one time, reducing the work flow. The grinding surface of the curved flap disc (T29) has an upward curvature, which gives the T29 flap disc a better cutting ability in the plane. When working, the T29 grinding wheel has an angle of 15° to 25° with the grinding surface. It is mainly used for grinding of contours and edges. When the speed and cutting ability have higher requirements, the T29 type flap disc is undoubtedly the best choice.