You will need one refill lead for a mechanical pencil that takes a relatively thick lead (the one in the image is for a 3mm Pilot Croquis pencil
- the refills come in tubes of two). I picked the B grade as its not too soft but will write on most surfaces. You will also need a piece of heat shrink tubing slightly bigger than the 3mm lead. The tube here shrinks from about 5mm to 2.5mm.