difference () {
cube ([10,40,40],center=true);
translate ([0,0,3])cube ([3.8,45,40], center=true);
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);
}