I work almost exclusively in the metric system. All of my metric taps and drills just sat in one of the drawers in your tool box. Now I can collect them all and put them in this index. Over the years I have collected drills and taps for all common metric threads. I also have standard hole sizes for standard metric taps. It would be great if someone made and indexed taps, taps and through-hole drills. What makes these indexes so useful is that you can see when a drill or tap is missing. As soon as I see a hole in the index, I order a replacement.