I took a film class in high school, and that little flip thing on the end of the spindle is what would hold your film reel on the rewinder.
https://www.google.com/search?q=anti...ie+film+winder
There are several here mounted in twos on boards. I think a film editor would need these to move the film back & forth.
I bet the clamp one (the OP's hand crank) was for movie theaters. They would only need one, to rewind the reel back so the beginning of the the film is in front, to send it on to the next theater.