The shelf stop in your refrigerator is what locks the shelf into the refrigerator liner. The shelf stop can be found attached to the shelf. To remove the shelf stop, begin pulling the shelf out until the stop hits the refrigerator liner, then depress the shelf stop to remove the shelf. With the shelf removed, you can simply slide the old stop out of its groove, and replace it with a new one. This part is made of white plastic and is about 1 inch in length. It is sold individually, and is an OEM part sourced directly from the manufacturer.