Lakeside thumb filler

For normal use, the hole in the barrel is covered by an internal tube which is connected to the section. The section is rotated to rotate the inner metal tube, thereby exposing the sac. This was also used on Century thumb filling pens.

The sac is protected by an internal brass tube.
Rotate the section vs. the barrel, and the sac with overlying straight bar is brought into the opening in the barrel.