Very interesting. Had never heard of Arkon. Thanks for the information.
It would appear you are using:
25mm Swivel Ball to C-Clamp Mounting Pedestal (SP25MMCLAMP)
then TWO of the above-mentioned extension arms (SPHDEXT)
followed by a 25mm Swivel Ball to 1/4"-20 Camera Mounting Bolt Adapter (SP25MMCAM) to hold the keyboard.