Set a 1.5" OD railing post to the floor with a tighter connection than a slip-fit gives you. The tube slides down into a precision-machined insert in the flange, so the post seats firmly and squarely on the base. It's a good fit for indoor rails on offices, mezzanines, and stairs where a clean, engineered post connection matters. The flange is carbon steel and works with.050" ultra-thin-wall tubing. Because it's carbon steel, plan on paint or powder coat if the rail goes outdoors. A spec sheet is available for engineering and code-compliance documentation.