It is mandatory that the punched or drilled hole you make in your metal, corresponds with the correct size of wire you are using for your rivet. If the hole is too big for the rivet, you won't be able to rivet them together. There are many ways to make holes in metal. Here are a few that I use: metal hole punches, Eurotool has a great hole punch with 4 different sizes of holes that correspond with wire gauge size, a Dremel with a drill bit and a flex shaft.
Pro Tip: Super Pro Tip: If you are using drill bits, it is so easy to get them mixed up or have to stop what you are doing and look up what size the drill number is for what wire size. I write on the package what size of wire to use with the drill bit.