$fn=100;

difference() {
    cylinder(2,7,7);
    translate([0,0,-0.5])cylinder(3,1.6,1.6);
}

difference() {
    translate([0,0,1.9]) cylinder(2.1, 3.5, 3.5);
    translate([0,0,2.7]) cylinder(  2,   3,   3);
    translate([0,0,1.8]) cylinder(  3, 1.6, 1.6);
}