Amazon.com: WORKPRO 10 Pack Grinding Wheels, General Metal Grinding Wheel for Metal, Stainless Steel, etc. Aggressive Grinding Disc for Angle Grinder, Type 27 Depressed Center Disc, 4-1/2" x 15/64" x 7/8" :
Type 1 vs Type 27 vs Type 29 vs Type 28 Grinding Wheels - Benchmark Abrasives