Originally Posted by polyglot
They're for transferring exposed film from the cartridge to the spiral, i.e. they are spiral loaders. They are not bulk loaders for transferring unexposed film from the bulk spool into the cartridge.
You can see in that picture several sizes - note the widths of the film tracks (the flat bit of metal) and the diameters of the little cartridge-holding sections.
Thank you for correcting me (post #8)!
I never saw these before and thought they were intended for darkroom spooling bulk film onto cartridge reels.