Our Advantage Zirconia Flap Discs are 4 1/2 inch diameter for small angle grinders.  They are 1/2 inch thick with resin coated paper backing. The 5/8-11 metal arbor hub locks for added safety. The zirconia flap wheels are ISO 9001 certified and capable of 13,300 Max RPM.  The 60 grit flap wheels are considered medium grit for zirconia.  They excellent for sanding and polishing steel.