It is a long story that was also a disaster. The one shown is my second attempt/version. I constructed the first one using a 16mm stainless steel rod and stainless steel screws. Sadly neither put up with the strain, and it collapsed onto the floor and damaged half of the discs. After speaking to structural engineer on another forum, I upgraded to a 26mm hollow stainless tube and thicker screws. Thankfully it worked the second time.