I was recently given an Agfa Isoflash-Rapid so have been doing a lot of research on the Afga Rapid cassettes. It appears the Rapid cassettes were designed for 12 full-frames, 16 squares, or 24 half-frames.
My particular camera counts down from 16 frames, and I had been pondering/lamenting the idea of processing such short rolls, but I came across some posts where other people have successfully loaded 24 full-frames in a Rapid cassette without issue. So the typical trick is to load a cassette, shoot a set, then just open the back and close it again to reset the frame counter, shoot the second set, and then process the batch either commercially or at home.
Some other people have found that some disposable cameras have a similar but slightly smaller plastic cassette that can occasionally be retrieved from a local minilab if finding Rapid cassettes is challenging. There doesn't seem to be good data on which models of disposables might have them, though.
The pin length on the metal T is to automatically designate the film speed for cameras that support it, and some may have ASA speed stamped into the T as well. ASA 80 seemed to be prevalent, and many people seem to have success shooting various flavors of modern ASA 100 film.
