Sait Long Life A24R are United Abrasives most popular grinding wheels.  Having a longer life requires fewer wheel changes.  They are made of aluminum oxide, a course grain size and a medium hard bond making them suitable for general purpose grinding.    Applications:  Ferrous Metals such as iron, steel and welds.  4 1/2" diameter, 1/4" thick, Type 27 (depressed center), and a 5/8" bore with hub.  For right angle grinders.