Crocker referred to this as a hatchet filler, thus some of the confusion with the John Holland hatchet filler. The difference being that the Holland pen has a piece that resembles a hatchet, and the Crocker really does not. But it is a clever way to have a nice big handle for the lever, and the knob also screws down to lock it in place. This is a lever you can easily work even if you just cut your fingernails.
Barrel end locked down 
Barrel end unscrewed 
Lever in action