I'm thinking he means what's often called the "oh crap handle". 04-08 have one on the driver and passenger side. Since the driver will probably only use it for getting in/out and not in an "oh crap" situation, assist bar certainly makes more sense.
IIRC it's 12mm. I loosened mine when I ran the microphone for my stereo. Although most of the time when I don't know what size socket to use I just keep trying them until one fits... it'd take a lot longer to work on my truck if I posted a new thread each time.