difference() {
    difference() {
        cylinder(r1=4.2, r2=4.2, h=5, $fn=50);
        cylinder(r1=3, r2=3, h=5, $fn=50);
    }
    translate([-5,0,10]) {
        rotate([0,90,0]) {
            cylinder(r1=7, r2=7, h=10, $fn=50);
        }
    }
}