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I did:
Arm - Threaded (x2)
Arm - Unthreaded (x2)
Short Arm - Threaded (x1)
Short Arm - Unthreaded (x1)
Knob (x7)
Everything Else (x1)

You can try more, but I haven't tried to test the breaking point. For each new section of Arm or Short Arm, you should just need 1 knob.
Note that, in the picture of it mounted to the wall, I had not added the short arms. So, to match the picture, do:
Knob (x5) and remove the Short Arm sections altogether.