The largest steel post-insert flange closes the line at 2" OD: the tube slides down into a precision-machined insert in the flange, seating the post firmly and squarely on the base — a tighter fit than a slip-fit allows. It suits indoor rails in lobbies, on mezzanines, and along stairs where a clean, engineered post connection matters. The flange is carbon steel and works with .050" ultra-thin-wall tubing; being carbon steel, it may need paint or powder coat before an outdoor install. A spec sheet is available for engineering and code-compliance documentation.