I have never taken one apart, but I will bet money the "fire bar" is an actuator, not a switch. There's probably a tac switch somewhere inside the box, and the fire bar has a post that actuates it. Take a look at the tac switch actuators at Fat Daddy Vapes, or they used to sell them, I haven't looked. Whatever, you can probably reuse what ever switch is on there, and if not, the specs for the switch should be on it.