A pencil refill cassette for your S. T. Dupont mechanical pencil The S.T. DuPont Pencil Refill .5mm Lead is a cassette which contains 0.5mm lead and has the eraser mounted on top. To be sure this fits your S.T. DuPont Mechanical pencil, confirm the dimensions of the refill cartridge already in your mechanical pencil. If you have any questions, please contact our customer service representatives.