They are called cleco's. They come in various sizes depending on what size rivets you are using. The four most common sizes are3/32 of an ince silver in color, 1/8 inch (copper), 5/32 of an inch (black) and 3/16 of an inch (brass,gold).You can order them from an outfit called aircraft spruce or maybe get some from an air conditioning duct manufacture. You will also need to get a pair of cleco pliers.