code: def get_mate_center(self, angle=0):
          
          return Mate(self, CoordSystem.from_plane(
              cadquery.Plane(
                  origin=(0, 0, self.width / 2),
                  xDir=(1, 0, 0),
                  normal=(0, 0, 1),
              ).rotated((0, 0, angle))  # rotate about z-axis
          ))
docs: Mate at ring's center rotated ``angle`` degrees.
  
          :param angle: rotation around z-axis (unit: deg)
          :type angle: :class:`float`
  
          :return: mate in ring's center rotated about z-axis
          :rtype: :class:`Mate <cqparts.constraint.Mate>`