difference() {
  linear_extrude( height = 30 ) hull() {
        translate([15,0,10]) circle( r = 17.5);
        circle( r = 17.5 );
    };

  translate([0,0,-5]) linear_extrude( height = 40 ) hull() {
        translate([15,0,10]) circle( r = 10);
        circle( r = 10 );
    };
}