Make a closed-end cap. When you drill the hole for the cap tube, add 1/8 of an inch. It is important to know where the tube ends in the cap - so measure exactly. After turning and before finishing make a measured mark like the tutorial says. Most of us don't have laser machines. You can use a very small drill bit or I use a small dremmel bit. Drill a hole in the middle of the mark - two side by side if necessary. I stay away from the outside edges of the mark and try to keep them toward the middle of the mark.
I then use an exacto knife to gently and slowly open up the measured mark until the clip (already cut as tutorial says) fits nicely inside. Set clip aside and finish the cap. Follow the rest of the tutorial.
If you don't want to press the metal part into the cap, I have found that packing wood dust or shavings (which I have plenty of) into the cap and adding med or thin CA glue works well. ***Make sure you don't allow the CA to come out of the slit in the cap*** this is a good way to ruin the whole thing really fast.
Don't know if any of that makes sense, but I hope it might help some.
Martin