$fn=100;

difference() {
    cube([80,28,3]);
    translate([25,3.5,1]) cylinder(2.5, 1, 1);
    translate([55,3.5,1]) cylinder(2.5, 1, 1);
}


difference() {
    translate([25,3.5,  3]) cylinder(4, 3.5, 3.5);
    translate([25,3.5,2.5]) cylinder(5, 1, 1);
    union() {
        difference() {
        translate([25,3.5,  5]) cylinder(2.5, 4, 4);
        translate([25,3.5,  5]) cylinder(2.7, 3, 3);
        }
    }
}
difference() {
    translate([55,3.5,  3]) cylinder(4, 3.5, 3.5);
    translate([55,3.5,2.5]) cylinder(5, 1, 1);
    union() {
        difference() {
        translate([55,3.5,  5]) cylinder(2.5, 4, 4);
        translate([55,3.5,  5]) cylinder(2.7, 3, 3);
        }
    }
}