This an early (post WW2) aircraft ejector seat launcher firing mechanism. 7" x 2 3/4". It has been cut away for instructional purposes. Pulling the hook part away caused the spring loaded striker to fire the launching cartridge (the brass cylinder). There were 4 of these launchers to every seat to be ejected. It was a violent event with risk of death and promise of injury. Modern ejector seats use rockets for a more gentle launch.