linear_extrude(2) {
  difference() {
    hull() {
      translate([-12,0]) circle(d=10, $fn=100);
      translate([12,0]) circle(d=10, $fn=100);
    }
    translate([-12,0]) circle(d=6.5, $fn=100);
    translate([12,0]) circle(d=6.5, $fn=100);
  }
}