United Abrasives- SAIT 20185 Type 27 7-Inch x 1/4-Inch x 5/8-11 Grade A24T Edge Depressed Center Grinding Wheels, 10-Pack A24T Edge Grinding. Aluminum oxide grain. Hard bond designed for edge and bevel grinding and other applications where a harder wheel is preferred. Longer life for fewer wheels changes. Ferrous Metals (iron, steel, welds, etc.) Virgin aluminum oxide grain assures consistent high stock removal for tough applications. All sizes are made with uniform grain throughout no filler grain used in the backing. All wheels internally reinforced with the highest quality fiberglass for maximum safety. Super-Lock Hub on all 5/8-11 threaded wheels is the safest, vibration-free design.