United Abrasives-SAIT 20173 Type 27 5-Inch x 1/4-Inch x 5/8-11 Grade A24R Long Life Depressed Center Grinding Wheels, 10-Pack For general purpose grinding. Longer life for fewer wheel 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.