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.  These zirconia flap discs are ISO 9001 certified and have a maximum RPM of 13,300.  They are 40 grit which is considered coarse for zirconia flap wheels.  The 40 grit zirconia will grind off light rust and slag from steel.