What function does the head button on a TREX V2 have? I had a crash a couple of weeks back and noticed that the head button was bent, so I removed it.

Fast-forward a couple of week to last night: I straightened the button and was trying to re-attach and the darn thing won't screw in! It only catches like maybe one thread and won't screw in all of the way. It looks like the cause 'might' be too much thread-lock, as I am getting stuff out when I dig around in there with an exacto knife.

Note, the button was VERY securely fastened when I thread-locked the head, so I did not remove it and re-thread-lock. It was this way from the factory.

Should I be concerned?

You'll live without it. The only function it has on my copter is to provide a spot were I can use my thumb to slow down the blades after I'm done flying. I didn't put it back on after it came loose and smacked a nice set of carbon blades during spool up. The only other use of the head button that I have seen is to fly inverted and skip the head button across the pavement.

its for carrying the heli, and stopping rotor (unnecessary on a 450) - also makes it easy to see that the rotor parts arent bent

so for flight it serves no purpose

Cool! I won't put a lot of effort into re-attaching it, then.

That Head button was probably the thing that saved my blades last time I crashed, full negative into the hardwood floor inverted... I don't know how, but I only had to replace my feathering shaft and main shaft...