This item serves as a “dummy” film spiral. Its purpose is to displace volume inside the tank. If you only want to process one or two rolls of film, most of the processing tank is empty. Therefore, it would be a waste of chemistry if you would need the full 500mL for a single film. With the displacer, you can process up to two films with only 250mL instead of 500mL! If you only process film occasionally, this can safe a lot of developer, and you also respect the environment.
