The fixture can adapt to various heights of the clamped object (in yellow) thanks to various angular positions between the blue hexagon and the green clamp bar.
To change the position: release the brown nut, move up the clamp bar, turn the hexagon and tighten the nut.
Pink and violet parts ensure good contact between the nut and the possibly slanting clamp bar.
The motion of the yellow object implies the change of its height.