Knowledge of pencils
How to fit the ball
It is a very small ball, and it is very strange why it is turning well without falling below. To make a chip, a thin wire-shaped metal is cut in a cylindrical shape, the end is truncated to a conical shape, a hole is drilled first, and the ball is put in it and beaten from the top. Then, the inside of the tube becomes a saucer shape and it is stabilized. Moreover, because the edge is closed along the ball (caulking), it is said that the ball does not fall.
