I knew I could create them using my hand-held circular saw. I have a photo of these posts at www.AsktheBuilder.com, should ...

It has a screw shaped end point. Not as clean cut as a twist or flat bit. It is used with a hand drill Wood Hole saw Comprised of a twist drill surrounded by a large circular tube with a saw teeth.

hand-cut aluminium alloy plate, nary a CNC tool in sight. The only unusual component is the saw blade itself, which might be a bit tricky to track down if you were so inclined to reproduce the build.