linear_extrude(2) {
  difference() {
    hull() {
      translate([-25/2,0]) circle(d=14, $fn=100);
      translate([25/2,0]) circle(d=14, $fn=100);
    }
    translate([-25/2,0]) circle(d=7, $fn=100);
    translate([25/2,0]) circle(d=7, $fn=100);
  }
}