So I'm looking to do the ultra minimalist key modification but am unsure on one point. Basically I would want a split ring though the holes of the keys so I could have them on a keychain and never having used pop rivets before I'm not sure whether you are left with a hollow tube or whether it is filled with the pin of metal that's left over. Simple question to answer if you know, but I don't! Hope someone can help me. Cheers.