These Adavantage Zirconia Flap Discs are 4 1/2 inch diameter for use on 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, made in Germany and capable of 13,300 Max RPM.  This 10 pack of zirconia flap discs for sale are 60 grit, which is medium coarse for sanding and polishing steel.