peg bar
A peg bar is a tool used in traditional hand-drawn animation. It consists of a metal bar with three pegs, and a hinged lid that snaps down on top. They are used with animation paper or painted cels which have been pre-punched with holes that fit the pegs. A stack of sequential frames can be stacked onto a peg bar and the artist can flip back and forth between frames as they raw, or flip through all of the frames to get a rough idea of the animation in progress.