This is a vintage Fairchild Moviepak Seventy 10 film and sound cartridge for use on Fairchild Galaxy players. 

This is an 8mm sound film loop in a cartridge that you would plug into a player, a pinch roller would raise up and move the film reel, while the usual tractor-gate would advance the frames, projecting the image onto a built-in rear-projection screen.

These were used a lot for in-store demo, travelling product demos, and educational uses. 

I'm not sure what this one is about, its labelled "Thompson Vibratory Mill" and from the short section i can see in the gate area, its nice and blue which means it must be some good quality stock that has not red-shifted.

See the photos for details of the actual item you are buying! 

Any other questions let me know.