difference () {
union () {
cube ([10,40,40],center=true);
translate ([15,0,-15])cube([20,20,10], center=true);
}
translate ([0,0,3])cube ([3.8,45,40], center=true);
translate([15,0,-15])cylinder(r=6,h=15,center=true,$fn=80);
translate([-5,0,0])rotate([0,90,0])cylinder(r=1.5, h=8, center=true, $fn=80);
translate([5,0,0]) rotate([0,90,0])cylinder(r=3.2, h=8, center=true, $fn=80);
}