Graham. explained on 20/11/2016 :
As it happened I salvaged one last week but I CBA to unthread the pile
so I cut the capillary tube.
I can't see any adjustment screw...
...Just dismantled it further and there is nothing to adjust. The
capillary tube enters the centre of what is best described as a
bi-metallic labyrinth with a plastic peg that presses against the
switch spring.

The manufacturer possibly sets the length of the plastic peg during
calibration or crimps the tube down to reduce the capacity..