Unlike a regular pencil, a carpenter pencil is not round. It will not roll away when it is set down.
A special sharpener can be used to sharpen the pencil to a point. It can also be sharpened with a knife. Because the lead is not round, the pencil can be sharpened to draw a narrow line, a wide line, or both. The pencil can be rotated to take advantage of the oblong shape of the lead. These pencils are also tough and can be used to draw on bricks or concrete. They are available at most hardware and lumber suppliers.