A five toothed ratchet mechanism soon to be implemented in card.

As the housing moves back and forth the pawl drops into the tooth and advances the gear one fifth of a turn before returning to engage the next tooth.

The second pawl, at the bottom of the picture, stops the gear from rotating back as the housing moves back to engage the next tooth. Without it the gear would just move back and forth.

USEFUL LINKS:
Two Tooth Ratchet Animation
Ratchet Mechanism
Ratchet Model (2)
Ratchet Model (3)