A nice picture with color that shows the construction of the half circles. The endplate on either side of bith halfcircles is made out of transparant acrylic, so light can pass through the layers and into the next halfcircle easily.

Also the straight bar of metal is clearly in view: this will fit into the other halfcircle steel core, center the half circle while placing and serve as mounting base for bolts to fit them together tigthly. This is important as one half circle is depending on its structural integrity by it.