The Piaget 9P is a 24mm diameter, 2mm thick, ultra-thin time-only no seconds movement. Its dial is only 0.3mm thick. Its barrel bridge, however, is a more conventional 0.75mm. In general, my impression is that the thinness is not due to the bridges, but to the very small vertical gap between wheels, which all have very short staffs, including the balance wheel.
Full movement
Bevelling on the barrel bridge
Crown wheel and its pivot
The main wheel is under part of the barrel bridge and over other parts
The click and its spring that ingeniously goes around the barrel bridge screw hole
Barrel bridge removed
Focus on the engraving
Train bridge removed
The main wheel is upside down and not in its position. This shows that its pinion is the same size and has the same number of leaves as the central pinion. As they are both driven by the barrel, they turn at the same rate.
The central pinion is held in place with a spring
There is very little vertical gap between wheels
Gear train wheels
Escapement
The balance wheel has a very short staff and almost touches the escape wheel
