- An early patent. I am not aware of a pen like this having been produced. The outer sleeve appears to be wider than the barrel, and slides off the end of the barrel.
2. Barrel is split, slides open. End is not attached to pen, and can slide off like a large blind cap. Long enough that it does not need to be fully removed to use the aperture to press on the sac
3. Barrel is split, mechanism prevents sliding portion from sliding off – Laughlin patent, perhaps the most widely thought of version
4. Three patents for Le Boeuf. The first is for a split barrel that slides open, similar to the Laughlin. The second and third are for versions where the entire barrel slides back to expose the filler.