what are the principles regarding pipe OD, thickness & strength as well regarding round and square which one is more stronger. This matter came up becoz there are certain sizes of OD not available in HR but only available in CR, on the other hand there are certain sizes which we can convert form round to square to save material or increase strength. Pls note that we have to find out the following regarding Pipes - 1. If we make a Hollow Round Tube of 15.88mm OD and 1.2mm Wall Thickness, means a weight of 470gm per mtr. Keeping the same weight per mtr, if we make Holow Tube of 19.08mm OD then its thickness will be 1.0mm. Now our question is, which Hollow Tube will be stronger? Which will bend less when put same pressure on same length? The Tube with 15.88mm OD or with 19.08mm OD as the material used in both of them is same?