You displayed a wooden bracket fixed to the TV and a rising pole tripod thingie. I envisioned one on pole to support the weight of the TV with a four inch neck or more extending up into the dowel hole of your wooden bracket.
Why? I suspect that the 1/16th or so edge where the pipe reduces at the top would not be sufficient to provide a comfy feeling for a heavy object on a wooden base. Swiveling or jiggling would begin to to dig into the wood. The clamp would not have that issue and also would add further adjustability. Alternatively adding an appropriately sized washer, countersunk into the bottom of the hole, could also prevent this problem as the edge would sit on metal. It might also increase the smoothness of swiveling, if desired.
If your riser tube was long enough, you could make the bracket hole go all the way through and put a 2nd clamp at the top to prevent someone from lifting it off of the bar accidentally and this could also be used to create additional pressure to prevent easy swiveling.
May not be the best solution, just the first one that came to my mind as i tend to think around what spare parts I have in my own garage.
