$fn =100; 
difference(){
minkowski()
{
  cube([40,14,11]);
  cylinder(r=2,h=1);
}

translate([1,1,-1]) minkowski()
{
  cube([40-2,14-2,2]);
  cylinder(r=2.2,h=10);
}

difference(){
translate([40/2,14/2,11-.5])cylinder(d = 5.5,  h = 8); 
translate([40/2,14/2,11-1])cube([5.5,4,4],center=true);
}
}