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 and doesn't back off like the 7/8 inch.  These zirconia flap wheels are ISO 9001 certified with maximum 13,300 RPM.  The 80 grit rating is fine for light sanding and polishing steel.