Question about the ARB air line and the the gear housing

There is a copper air line for my ARB locker. Where it runs up to the top of the gear housing, how far does it need to stick up through the hole with the o ring? Sorry I can't describe it better but it's where the plastic line mates to the hard line inside the housing.

It varies,they changed the design a few years back,Go to their website and donwload the instructions if you don't have them.

Yes, you need the instructions for the bulkhead fitting.