Product review (3 stars): Overpriced
These tiny pieces of rubber are notoriously easy to lose or break when the grates are moved, and Ive bought many of them over a period of 13 years.  My solution was to buy a tube of Permatex Ultra Black Gasket Maker.  Put a little glob of this on the foot, let it dry overnight, and you're done.  Adjust for size if necessary.  For about $5 I have a lifetime supply of little feet!  Wish I had discovered this solution years ago.