Product review (5 stars): Works as specified
The caps are simple and work as advertised.  I found that, for severely rusted rack ends, I needed to trim off about a quarter inch of the swollen, rusted end with a pair of heavy nippers prior to installing the caps.  I also put a small dab of clear epoxy (available at any hardware store) inside each cap with a toothpick prior to installing them.  It's been a couple months now, and the caps have all stayed in place.  The result is that I've extended the life of the dishwasher rack and, so far, inhibited the formation of more rust at the rack ends.