This is part V as labeled in jeepguys assembly instructions. It is what the spring and washer sits on to apply pressure to the filament.
I found that the center slot for the long bolt HW04 was too narrow and would bind up. I suspect this would give intermittent feed issues. This part was made to widen that slot.
Extended the plastic a bit to make it easier to pinch by hand to remove pressure from the filament.