Aluminum oxide grain.Open pattern on wheel for cool grinding and blending.Contaminant Free ????????????Safe for use in the nuclear industry.Use for longer life in aggressive applications.Must be used with backing pad (one included in each box)., Type 29 shape allows easy control in grinding and blending applications.Honeycomb, dimpled pattern on face allows for greater cooling and longer life.Grind and blend welds in one-step, no need for multiple steps and products.Ideal for grinding radius and contours in pipe and vessels.Each box of 25 is supplied with a backing pad and one 5/8-11 nut. Additional pad assembly: 4-1/2" & 5" - part #95245 7" - part #95254.