This is a pen I made a few weeks ago, as a response to a challenge from a friend. The challenge: make a fountain pen with a slip cap, rather than a screw on cap. This is what I came up with. It’s is made from a light blue transparent acrylic, with silver trim and clip. It is threaded for a Pelikan m1000 nib unit, and fills via eyedropper, by unscrewing the nib. I used an o-ring to allow the cap to slide on the barrel securely, without scratching the barrel. The slip cap works quite well, and is secure with no wobble. This was more a proof of concept, and if I were doing it again I would change a couple things, primarily making a removable section, which would allow the pen to be used with a converter (although not with this particular nib), and experimenting with putting the o ring inside the cap rather than on the barrel. At any rate it was a fun project, and my friend is happy with it.