When the hand is not a pencil of suitable color or hardness. would be useful and “bits”, but they are inconvenient to use, they can be extended by sticking in a metal or plastic tube of suitable diameter. However, even that would be smeared, equal to the thickness of the pencils the size range — one enters too freely, the other will not wedge. I use a tube extender with internal thread M8: it holds round and hexagonal crayons.
S. KUSMARTSEV, Volgograd