When the clutch pedal is pressed, a cable or hydraulic piston pushes on the release fork, which presses the throw-out bearing against the middle of the diaphragm spring.

The 'Down Chain' rides inboard of the bearing, and moves with the fork.

The fork moves the release bearing into the center of the pressureplate. This causes the pressure plate face to pull away from the clutch disc, releasing thedisc from the flywheel.