difference(){ translate ([0,50,-1]) cube ([26.5, 26.5, 3], center=true); #translate ([0,50,-5]) cylinder (h=30, d=9.4, $fn=30); translate ([0,50,-1]) cylinder (h=30, d=12.6, $fn=30); //holes translate ([9,41,-5]) cylinder (h=30, d=3.2, $fn=30); translate ([-9,41,-5]) cylinder (h=30, d=3.2, $fn=30); translate ([9,59,-5]) cylinder (h=30, d=3.2, $fn=30); translate ([-9,59,-5]) cylinder (h=30, d=3.2, $fn=30); }