Mechanical, or automatic, pencils solve the problem of pencil sharpening by using constant thickness lead that is not attached to the pencil itself. Pentel mechanical pencils come in a variety of different models, and can use either graphite or Pentel's high-polymer lead. The lead refilling process is similar for most designs, so it is easy to replace the lead when you run low.

Check the side of your mechanical pencil to find what size lead it takes. The size will be given in millimeters.

Pull the cap of the pencil off. The cap is the part that holds the eraser. Some models may require you to rotate the cap in order to remove it.

Insert new lead and replace the cap until it locks into place. Press the cap down several times to ensure the lead advancement mechanism is not blocked.