radius = 12.25;
len = 60;
wall = 4;

screw_radius = 2.5;

difference() {
    union() {
        cube([len, (radius+wall)*2, radius+wall]);
        hull() {
            translate([screw_radius+wall, -screw_radius-wall, 0]) 
                cylinder(r=screw_radius+wall, h=wall);
            translate([len-screw_radius-wall, radius*2+wall*3+screw_radius, 0]) 
                cylinder(r=screw_radius+wall, h=wall);
        }
        hull() {
            translate([screw_radius+wall, radius*2+wall*3+screw_radius, 0]) 
                cylinder(r=screw_radius+wall, h=wall);
            translate([len-screw_radius-wall, -screw_radius-wall, 0]) 
                cylinder(r=screw_radius+wall, h=wall);
        }
        translate([screw_radius+wall, -screw_radius-wall, 0]) 
            cube([len-(screw_radius+wall)*2, screw_radius+wall, wall]);
        translate([screw_radius+wall, (radius+wall)*2, 0]) 
            cube([len-(screw_radius+wall)*2, screw_radius+wall, wall]);
    }
    translate([-1, radius+wall, radius+wall]) rotate([0, 90, 0]) cylinder(r=radius, h=len+2);
        translate([screw_radius+wall, -screw_radius-wall, -1])
            cylinder(r=screw_radius, h=wall+2);
        translate([len-screw_radius-wall, radius*2+wall*3+screw_radius, -1])
            cylinder(r=screw_radius, h=wall+2);
        translate([screw_radius+wall, radius*2+wall*3+screw_radius, -1])
            cylinder(r=screw_radius, h=wall+2);
        translate([len-screw_radius-wall, -screw_radius-wall, -1])
            cylinder(r=screw_radius, h=wall+2);
}