Materials required:
Cut brass tubes
Finished bases
Superglue (Cyanoacrylate)
Cut steel rod
Hobby knife
Magnets
This step involves cleaning the brass tubes so that the smaller tubes fit snugly into the larger tubes, attaching the finished tubes to the base, and attaching a magnet to the end of the steel rod.
If you recall from the last step, after the tube is cut, there remains a flange (see previous picture) on the inside of the tube. This flange will prohibit the fitting of the tubes together, and therefore must be cleaned off.
Start with the largest tube. You will have to clean both ends. One end will fit onto the base (end A), and the next smaller tube will fit into the other end (end B).
Start with end A, where the rod will fit onto the base. To remove the flange, simply carve it away using a hobby knife until it fits onto the screw projecting up from the base.
(A small diameter reamer, if you have one, works better.) Fit is not critical here, as we will secure this rod to the base using CA glue in a later step.
Then clean off end B. In this step, it is important that some of the flange remain in order to form a snug fit to next smaller tube. Work carefully and test for fit periodically.
If you find that you cut away too much of the flange so that the fit is not snug enough, don't worry. Using a small pliers, gently crimp the edge of the tube. But be careful not to deform the tube too much, or else the smaller tube won't fit.
Follow the same procedure (as for end B above) for the remaining tubes. However, only one end of each successive tube needs to be cleaned. You can clean off both ends, but it is not necessary.
When fitting the steel rod to the last tube, you may find that it is difficult to get a snug fit. If so, you may want to introduce a slight bend into the steel rod. To do so, grasp one end of the rod with the pliers. Apply pressure with your free hand, gently, and slightly bend the rod. The bend should be as close to one end as you can make it.
Then insert the bent end into the brass tube.
Once the rod and all the tubes have been cleaned and tested for fit, it is time to attach them to the base. Lightly coat the screw on the base with CA glue, and then slide only the largest tube onto the screw.
Set aside to dry. Once dry, fit the remaining tubes together.
Lastly, you'll fix a small magnet to the end of the steel tube. It is important that the orientation of the magnets' polarity be consistent throughout your bases. The best way I found to do this is by using a miniature with its magnet already attached. Simply attach another magnet to the miniature. The new magnet will only attach itself in one direction, so you can't mess this up. Next, place a small drop of CA at the tip of the rod, and place the aircraft with magnets on it. The magnet itself will help you place it on the rod, and hold it in place until dry. Using this method for all your bases will ensure they are compatible with all of your aircraft models.