spacer_thickness = 3;

hole_diameter = 3.5;
hole_spacing = 31;
center_hole_diameter = 24;
outside_width = 42;

$fn = 100;

difference()
{
    cube([outside_width, outside_width, spacer_thickness],center = true);
    translate([hole_spacing/2,hole_spacing/2,0]) cylinder(d=hole_diameter, h=spacer_thickness, center = true);
    translate([hole_spacing/2,hole_spacing/2*-1,0]) cylinder(d=hole_diameter, h=spacer_thickness, center = true);
    translate([hole_spacing/2*-1,hole_spacing/2,0]) cylinder(d=hole_diameter, h=spacer_thickness, center = true);
    translate([hole_spacing/2*-1,hole_spacing/2*-1,0]) cylinder(d=hole_diameter, h=spacer_thickness, center = true);
    cylinder(d=center_hole_diameter, h=spacer_thickness, center = true);
}