Figure 3 shows the mechanical assembly. The three
different sized rings are inside each other. There are rods and
screws to keep them together while still allowing them to bend
according to one of the three axes. In this way, the rings cannot
rotate or slide. There are covers on the rings like hub caps to
form a sphere-shaped volume and to concentrate the force on
only one point. Actually, the rings are compressed, so there is
an associated area with the force (N/m2).