difference() {
  // Mold inside
  square(51, center=true);

  // Cutouts
  translate([51/2, 0]) square([16, 28], center=true);
  translate([-51/2, 0]) square([16, 28], center=true);
  translate([0, 51/2]) square([41, 6], center=true);
  translate([0, -51/2]) square([41, 6], center=true);

  // Binding posts    
  translate([0, -12]) circle(d=4, $fn=100);
  translate([0, 12]) circle(d=4, $fn=100);
}