Camel CGW brand 4 1/2" diameter high performance grinding wheels ZA24T are made of Zirconia and Aluminum Oxide grain, allowing for faster and smoother grinding as well as an extra long wheel life. Available with a depressed center (Type 27). Grain Size: Course. Grade: Hard Applications. Great for hardened, alloy steels and stainless steel. With and with out locked on hubs, for angle grinders.