What can I say, theyre end caps. Buy a set cause they are great to had when one falls off or gets stolen. Also, without them, your rack could be noisy and cause some wind resistance when driving.

These end caps are usually taken for granted until one goes missing. Without this, your rack can be really loud, especially on the highway, as well as create drag. Make sure you get the right ones for your crossbars. Its always nice to have a couple in your glove box just in case.