This chalk holder is designed for use with 9 mm chalk. It has teeth near the end that lightly grip the chalk to prevent it from sliding. When held in your hand, the pressure from your fingers tightens the grip so the chalk does not move.
By rotating the threaded rod, the chalk is pushed out as it is used, while the threaded rod also provides additional support to prevent the chalk from slipping back into the holder.
The author remixed this model.
A threaded hole is made in the basic model, and a threaded rod is added to support and push the chalk out of the holder.