Surface-conditioning wheels are made of nonwoven material with an integrated abrasive to clean and prepare surfaces for finishing. They install on grinders and rotary tools to remove surface imperfections like rust, mill scale, paint, and light scratches. Surface conditioning abrasives smooth and prepare surfaces for finishing in a single step rather than requiring multiple grits of sandpaper. Convolute wheels are flexible to conform to the workpiece and are often used for centerless grinding for final finishing. They're unidirectional and marked with an arrow to indicate the direction of rotation. Unitized wheels are harder than convolute wheels, making them a better choice for removing scratches and surface imperfections. Unitized wheel are nondirectional.