inner_hole_dia = 14 + 0.5;
mid_hole_dia = 30 - 0.5;

outer_dia = 40;

height_step = 5;
height_step_small = height_step/3;

$fn=150;

difference() {
    union() {
        translate([0,0,-height_step_small])
        cylinder(r=mid_hole_dia/2, h=height_step+height_step_small, center=true);
        translate([0,0,height_step_small/2])
        cylinder(r=outer_dia/2, h=height_step_small, center=true);
    }
    cylinder(r=inner_hole_dia/2, h=height_step*2+0.01, center=true);
    translate([0,-20,-20])
    cube(size=[40, 40, 40], center=false);
}