As far as I can tell one manufacturer uses fractional bit sizes while the next uses Metric and some use Letter. It also seems to me that the actual drill bit suggested is at best a close enough type thing. I find that this Close Enough approach results in some kits with loose fitting tubes. Others with tight fitting tubes. More often than not if I want a tube that fits well. I select the correct bit for myself. In some cases the difference between a fractional, Letter or Metric bit is so small as to not really matter. For example a 7mm, and I think a J bit are only a few thousandths of an inch different. this is really not enough to matter. At one time there was some discussion about putting together a recommended real set of drill bits but I found that while one person wanted a snugger fit the next person wanted a looser fit. The problem really came down to this. Lets say for example (I don't have drill bit chart in front of me) A 7mm, J and 7/32 drill bit are really the same size bit for our purposes. Bit Person A thinks the 7mm is the best one to make the standard and person B thinks it should be the J and then Person C thinks it is the 7/32. And each can give equally good reasons for their choice. What came of it all is mainly to do what we can to inform people that some sizes can be used a substitutes but you will have to decide for yourself which is the best choice. For me, I simply bought all of them for about $100 and don't have to worry about having the best bit anymore.
