The Parker pen company offers a line of mechanical pencils that are refillable with double-length lead. The led is extended through the mechanical pencil by twisting the cap to extract the lead to your desired length. Lead refills are added to the pencil by turning the cap clockwise until it clicks, indicating that the lead has cleared the tube. Turning the cap counter-clockwise until you hear another click will reveal a hole to insert the lead into the pencil.
Twist the cap to the right until you hear a click indicating that the the tube is free of lead.
Twist the cap to the left until another click is heard and a hole is exposed at the top of the pencil.
Place double-length lead into the hole near the cap. You can insert up to six pieces of lead in the Parker mechanical pencil at one time. Use your finger to push the lead down into the hole, making sure it is set all the way through the hole.
Twist the pencil cap clockwise to close the hole and extract the pencil lead about 1/8-inch. Lightly push the tip of the Parker mechanical pencil against a flat surface to secure the lead into the clutch tube.
Twisting the cap to the right will extend the lead. Turning the cap to the left retracts the lead back into the pencil.