Hi Pilou,

> I have not follow but a simple Extrude by Dir for the internal cylinder
> don't make the trick ?

That works too, but it will create a surface that has a kind of slanted structure to it. That's not too bad but it's kind of nice for a cylinder to be represented by the extrusion of a circle that is perpendicular to the cylinder's axis just to have the most simple kind of end result that would match up with an analytic cylinder primitive.

- Michael