There's 3 taps in this set. Not because you need 2 spares, it's because you need step 1, 2 and 3. Just easier to do it this way when tapping manually. Start with the more "tapper" first. This is the #1. (most important for what you need to do) You should finish it up with #2. #3 is a bottom tap. When your hole doesn't go thru... So you can make threads all the way to the bottom of the hole.
Have fun! Hey, don't forget the lube with Aluminum!!! Good old WD-40 do a great job for aluminum. If you can put your hand on some rapid tap it's even easier. Make sure it's for Aluminum, NOT STEEL!!! Go back and forth 1/4 turn at the time max, you need to "brake the chip" Don't be afraid to pull it out every turn or two to clean it up too. If you try to go too fast (get hot) it might rip the threads off. Take your time, keep it cool, keep it clean and keep it lubed!