$fn=40;

 difference(){
     cylinder(d=100,h=10);
     translate([-20,20,0]) cylinder(d=15,h=10);
     translate([20,20,0]) cylinder(d=15,h=10);
     difference(){
            cylinder(d=80,h=10);
            translate([0,15,0]) cylinder(d=90,h=10);
     }
}