Amechanical pencil(US English) or apropelling pencil(UK English) is apencilwith a replaceable and mechanically extendable solid pigment core called a "lead". Thelead, often made ofgraphite, is not bonded to the outer casing, and can be mechanically extended as its point is worn away. Other names includeautomatic pencil,drafting pencil,technical pencil,click pencil,clutch pencil,leadholder,pen pencil(Indian English), andlead pencil(Bangladeshi and American English).
Mechanical pencils are used to provide lines of constant width without sharpening in technical drawing and in quick, neat writing. They have also been used for fine-art drawing. They are also popular with students, since they do not have to be sharpened. Mechanical pencils were first used in the 18th century, with many designs patented in the 19th and 20th centuries. Source : Wikipedia