This nifty device is a wooden holder the exact size of a 4x5 film holder, with different sized frames that slide into the holder. The frames are made of sturdy plastic. I believe they were used for composition when photographing two groups of people, or for bracketing on a single sheet of film. The frames will not fit a regular film holder, so you'll still need to cut up a dark slide, using the frames as guides. Note that the large frame will not fit into the holder, because it is too thick.