Thanks!
About drill bits, basic metal working bits will probably be sufficient. The hollow copper rod was a bit more difficult. (As in getting it to stay in place.)
About the clamp, it goes on top. Copper to right, zinc to left as it is advised. I "designed" it to be worn on top, the clamp section. I haven't had irritation, the fit is snug but the string doesn't creep into the skin. Very comfortable altogether. The bottom part, where the silicone part is, I did try several different types of ways. Just string; creeps into skin, uncomfortable. Silicone bits covering the rod ends; still creeping and discomfort.
It was yet a measuring issue to get this to work, I needed to insert the silicone further to the copper so it stays put. (So, in the beginning I had not cut the silicone part long enough.)
Good if this inspires anyone!