A 10 pack of our Advantage Zirconia Flap Discs.  They are 4 1/2 inch diameter for small angle grinders and have a 5/8-11 arbor that doesn't require a retaining nut.  The 5/8-11 arbor doesn't back off and have to be retightened like the retaining nuts.  This set of 10 zirconia flap wheels are 40 grit which is considered very coarse for grinding and sanding on steel.