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Dearest MacGiver, the word "parametric" means that this is a design that will adapt and change shape according to parameters that you supply. Parameters such as inner diameter, outer diameter, wall thickness, tolerance and so on. The easiest way to study this in practice is to try the "Open in Customizer" link on this page. This is not a matter of scaling, the entire design (number of ribs and shape etc etc) changes according to the parameters you supply. I believe "parametric" is the most appropriate term to describe this.