I fit/inlet mine so tight that they don't really need a rivet. Once it's on, you need a screwdriver to pry it off. The natural springyness of the cap holds it on. On the final installation, I put a dab of Permatex Form-a-Gasket inside the cap, spread it around, and shove the cap on. The Permatex bonds it, but never hardens so it can be removed in the future, should that ever be necessary.