Round steel structural columns with base plates welded to the top and bottom are another option. The most cost effective steel post is 4.5” diameter with 1/8” thick walls. Many of these are part of an assembly for a decorative columns. Steel is rarely used in residential deck construction because it is expensive, not readily available and more complicated to install. If you do choose to use steel be sure to check it out with your building inspections department and follow the manufacturer’s installation instructions.