This model shows the oscillating mechanism of a fan. The long shaft is connected directly to the fan blades (not shown) and the large step in the shaft represents the motor. The shaft is driving a worm gear which has a smaller gear connected below it. This smaller gear is meshed with a bigger gear and a link is connected to the outer radius of the bigger gear. The other end of the link is restricted to only move in one direction, causing the link to oscillate.
When the pin isn't pressed down, the gears aren't in contact with each other and only the shaft controlling the blades will be rotating. This is representative of the fan being on but not oscillating.
When the pin is pressed down, the gears are moved into place and the fan begins to oscillate.
