This pen is my own somewhat crude invention. It is made from a PenBBS standard twist piston. I wanted to make a pen that allowed for maximal travel of the piston, but with a more simplistic construction than the Bulkfiller. My design is like the Reform “wand filler,” but I would possibly call this design the “key filler” where the piece in the clip is the “key” for operating the piston. My idea was originally for the clip to detach and serve as the piston rod. This evolved into a detachable rod that is stored inside the clip. Scroll down for a video of how it works.