There are five buttons you might see on vintage pens: plastic, top hat, twist, aluminum, and brass. Plastic and top hat buttons were used in cheaper pens. The twist button was used in Mabie Todd Swans and Blackbird pens. The aluminum button was found on postwar Victory and Duofold Parkers. However, the brass button was most popular.
Button-fillers also required a button bar to operate – when the button was depressed, the bar would compress the sac and draw a vacuum, so it functioned similarly to a lever-filler.