So, I'm finally considering trying one of these actuators in the pneumag i have here. But when I search for it, I usually see something like this:

Even after finding some other pictures around the net, it seems impossible to get an idea of what/where this moving part/piston is that will be responsible for tripping the sear. Can anyone clue me in on whether this is included somewhere or if i need something else?
note: i'll be using a 3way solenoid with this ram/actuator.