Precision machined surface. Hard surface tension. Perfect for curved sanding. Flexible. Patented This is the "Round" style block. Used to sand and block highly curved surfaces. L-11", Thickness 1-1/4" Uses 9" X 11" sanding paper. Perfect for those hard to get contours, inside and outside curves and areas which cannot be finished with standard flat pads. Its hardness and flexibility allow for a smooth flat surface.