I ordered a table made from this material this week for my 25.4 inch MPCNC with a 4x4 foot working area. (5x5 foot frame)
I will submit adapters for the 28.5 inch tubing to one inch tubing in the racking once it arrives and I can put the calipers on it and get a good measurement of the ID of the racking.
It is locally manufactured here in the Philippines for export. Used in Japanese car assembly lines and electronic factory assembly lines.