Lead Diameter
The thickness of the lead (writing rod) in a pencil or each crayon in a set (see "Product Type").
The meaning of this parameter depends on the specs of the pencil. So, in traditional pencils (lead in the casing), the thickness of the lead determines only the maximum thickness of the line that can be drawn in one pass. In collet models (see above), this parameter is also necessary to search for refill leads: their diameter must correspond to the size of the lead slot of the collet. And interchangeable leads with a diameter of more than 2 mm, usually, also have to be sharpened. However, anyway, each size is good for its tasks: thin leads are convenient for precise small work, and for large volumes of shading, it is desirable to have thicker pencils — they are not only more convenient, but also do not expend so fast.
As for the crayons, their thickness primarily determines the ease of use, as well as compatibility with special collet pencils that play the role of holders.