I'm baffled. I just looked through the mounts at Peerless's site and the mount is not there. It looks very much like the ST650 or ST660 but none of the three mounts used in this place has the crank that's used to cinch the mount to a particular angle.
The mounts we have don't have anything to pull down to release, either. Baffling.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw