$fn=100;
cube([55,55,3],center=true);
translate ([20,-22.5,0])cylinder(11,2.4,2.4);
translate ([-20,-22.5,0])cylinder(11,2.4,2.4);
translate ([20,22.5,0])cylinder(11,2.4,2.4);
translate ([-20,22.5,0])cylinder(11,2.4,2.4);