Silicon carbide grain for long wheel life in all masonry materialsHigh grain concentration for agressive grinding action and smoother running wheelsProprietary wheel design ensures durable long life wheelsDiameter 4-inch, edge thickness 1/4-inch, arbor size 5/8-inch. Grit C24R. Max RPM is 15,200.3 full sheets of glass in every 1/4-inch wheel and 2 full sheets in every 1/8-inchwheel for added durability and safety