difference() {
union() {
translate([0,0,6]) cylinder(r=5.1, h= 12, center=true, $fn=80);
translate([0,0,17]) cylinder(r=7, h= 13, center=true, $fn=80);
}
cylinder(r=4, h=80, center=true, $fn=80);
translate([0,0,20])cylinder(r=6, h=10, center=true, $fn=80);
}