Thank you, just has a rubber sac and typical pressure bar that is depressed by inserting anything that fits to push in the bar and compress the sac, then the ring is rotated over the hole. Just before and after Sheaffer's invention of the lever it was used in some pens like Aikin Lambert, not sure if Waterman did, they had a sleeve that slid toward the pen end to expose a bar that could be depressed by finger pressure as it had a metal button under the sleeve and a bigger opening for finger pressure. Keene had a pen like this that I have, and it has a clip that can be moved toward the cap lip so the ball of the clip can be used to push the bar, another early maker had a post on the end of the cap that could be used. They are today referred to as matchstick fillers as a group. Long explanation....sorry