This style is the first version of the Betzler accordion sac fountain pen filling pen. A flat piece flips out of the middle of the rod to make the rod longer for deeper compression of the sac while maintaining a shorter blind cap when the filler is not in use. If I have not described it well, picture how the blade flips out of a folding knife, but the “blade” is the extension of the compressing rod. Press inward to compress the bellows of the accordion sac and release. Then fold the rod extension back into its storage slot. I could imagine why this is less stable and less sturdy than the “new” or “perfected” version. I have seen surviving original Betzler fillers of the extending rod type, but not this one.