Homebrew PCBs

Hi,


My drills are all without the little plastic rings, so i bought a small  
lot with rings in the hopes of using them.
How can those rings be set? does it work with a metal tube and a little  
hammer?

Also, if somebody knows a inch/metric PCB drill conversion table (with the  
#), please let me know. it isn't that important as i can easily calculate  
it myself, but if you know a url...

ST