Mechanical pencil

Cut in half lengthwise. Press Click, or click the cap, and watch the lead creep out.

1. The button pushes the lead tube and chuck forward. The closed jaws carry the lead along.
2. The clutch ring hits the stop in the tip. The lead has moved 0.5 mm.
3. The jaws keep going, slip out of the ring and spring open. The rubber retainer holds the lead.
4. Let go. The spring pulls the chuck back. The open jaws slide back along the lead.
5. The jaws pull the ring back to its seat and close. The lead stays 0.5 mm further out.