$fn=128;

height=25;
outer=21;
inner=20;

difference() {
    union() {
        cylinder(h=height,d=outer);
        cylinder(h=3,d=outer+5);
    }
    cylinder(h=height,d=inner);
    translate([-10,0,height/2]) {
        cube([10,2,height], center=true);
    }
}