Would these work for I tip extensions? If so which one would I need the 5 or 7 tooth?

Depends on which installation methods - I really only like these for fusion where you need to allow for space near the roots and to not burn the client's scalp. If you are using I-Tips for Linkies or Shrinkies - they are okay, but I find them to be a bit cumbersome for the time that they save.