The second knob is a second lock that slides up to cover the liner lock and prevent it from moving sideways.

The original Air Ranger does not have this second lock, and is also significantly smaller in size--blade length is 3.25" I think. Of course the Air Ranger II came out right after I bought my Air Ranger, so I went ahead and got both.

BTW, where did you get the black Air Frame? I've only seen the original tianium handles and the later brushed aluminum, never black. It looks really nice!

Oh yeah, and I never carry a knife to a rock concert for the possibility of getting into a fight. It's more of a peace of mind thing for if some disaster should strike the venue. I used to work on stage crews, and with all those wires and ropes around, not to mention bizarre stage setups, if one of those things were to come down, or if you needed to leave the building in a real hurry, you might need to cut your way through something...inanimate, hopefully...