slashSTI, the holes in the door are square about 1/4 of an inch. The grommet will fill this hole and allow you to use a screw. I didn't have these so I got some nuts bolts from HD and just used some nylon washers to hold the speakers to the door. No big deal since you have to use adapters anyway. Use the grommets if you can as it it very hard to get your hand behind the door panel where the tweeters go. I would think you can get them from a dealer.
TweetyBird, there are many many threads about this topic on the internet, on this site and several others. Try doing a little searching before asking very general questions. That's why you got little response.