Internal worm is the grey ring. In fact it is a nut (1 start) engaging with green gear (40 teeth). Tooth shape of the green gear is not the one of ordinary spur gears.

Input is pink pinion (10 teeth) engaging with yellow large internal gear (60 teeth).

The grey ring and the internal gear are fixed together.

Output motion is taken from the green chain sprocket.

Total transmission ratio: (60/10).(40/1) = 240.