Product review (5 stars): Lifesaver...from rust spots on my dishes!
UPDATE 5/19/16: Just a few months later and these little guys are still doing great. No discoloration, no popping off, working like they should.

These little guys are great. We had over 20 rusting dish rack tips leaving rust marks in the back of our dishes. These little covers are small, so small they didn't fit over the rounds tips of the rack. I thought I maybe bought the wrong size. Here is the trick to get them to fit...boil them in water for about a minute.

I put 4 in the boiling water at a time and then took them out one-by-one. You can handle them...they will just feel warm, but now the plastic/rubber is flexible. Make sure to blow into each cover to get the water out. Push onto the rack tip, then wiggle them down. Using dry fingers or a dry rag, grip the cover and push it down to stretch it out a bit.

We'll see how well they do over the next few months.