Grado refrence arm help...........

Hi all,
I have this arm mounted on a SOTA, I got an instruction book from Grado but some of the instructions are not complete.
What I cant figure out is exactly were the adjustment is to fix the arm in place, it is mounted to the table but the center of the arm can be lifted out by hand and it spins freely, does anyone know how to tighten down the arm so it can be set-up?
Any help would be great, thanks Chad
I had one of these arms many years ago. There is a set screw to tighten some where very low on the post. Keep looking around until you find it. Do not tighten to hard, as the screw can pierce the pole in the post. Don't remember much more. Call Grado, I'm sure they can help you.