def make_simple(self):
        """
        Return a cylinder with the thread's average radius & length.

        :math:`radius = (inner_radius + outer_radius) / 2`
        """
        (inner_radius, outer_radius) = self.get_radii()
        radius = (inner_radius + outer_radius) / 2
        return cadquery.Workplane('XY') \
            .circle(radius).extrude(self.length)