These Advantage Zirconia Flap Discs are 4 1/2 inch diameter for small angle grinders.  They  are 1/2" thick with resin coated paper backing. The 7/8" arbor hole has a durable metal outer layer.  Advantage zirconia flap wheels are ISO 9001 certified and have a maximum RPM of 13,300.  The 80 grit flap wheels are fine grit for very light sanding and polishing of steel.