The Firepower 1423-2191 Type 27 Depressed Center Grinding Wheel with Hub measures 7 inches x 1/4-inch x 7/8-inch. Firepower depressed center wheels are fully reinforced with resin-bonded aluminum oxide to ensure safety at high speed and to increase bonding and impact strength. Designed for use on air- or electric-powered right angle or vertical shaft grinders. Maximum RPM: 8,500. Grade A24R.