Use 3 3mm socket cap screws (length depends on how many keys you want to use) and nuts (sized for 3mm nylocks), assorted washers. Using washers will make the keys easier to pull out and get a decent snugness. But you could lose them if you wanted a smaller overall thickness.
Swiss Army style keychain version 2 by outcastrc is licensed under the Creative Commons - Attribution - Non-Commercial license.
