Bullard Turbo TYPE 27 Depressed center grinding wheels, Aluminum oxide grain. A Size: 9 x 1/4 x 5/8-11, (20968 9 x 1/4 x 5/8 11 AZ4N 10 per box) Application/Material: Metal Fast Grind, Max RPM: 6500, Main application - ferrous metals (structural steel, iron, welds). Superior stock removal and wheel life verses general purpose grinding wheels