The sleeve filler was not one of the more common fillers used in the early fountain pens.
In this variation, the sleeve fits over the barrel and covers an exposed pressure bar.
I started by looking at some early sleeve filler pens. I didn't like the fact that the sleeve would be friction fit to the barrel of the pen when fully closed or fully open. That would basically scuff up the barrel a bit more each time it was used. And it also meant that it could potentially slip.
I wanted something more secure, so on this pen I put a touch of four start thread in the center of the sleeve — just enough to tighten when the sleeve is closed, but also to hold it open when filling so the sleeve would not fall back. The result is that it's not sliding on the barrel and scuffing the finish.
The pressure bar is curved brass with a textured button added to provide the ability to more easily press the bar down fully
I found a small block of hardwood tucked away on a shelf in my shop and the color of the wood seemed to complement the colors on this pen.