Thanks, vanark. I believe I see it now.
The articulating arm attaches by one of its spigots, just like I've tried it.
And I've got the stud, the hexagonal piece with a 1/4" screw at the end. I just tried securing the stud to the bottom of the 099B, tightening it with the set screw, and then the stud slides into the clamp. Great!
Thanks again.