radius = 8.25;
wall = 4;
len = 60;

rotate([0,90,0]) difference() {
    intersection() {
        cube([(radius + wall)*2, (radius + wall)*2, len], center=true);
        cylinder(r=(radius + wall)*sqrt(2)-2, h=len, center=true);
    }
    translate([0,0,len/2+wall/2]) cylinder(r=radius, h=len, center=true);
    translate([0,0,-len/2-wall/2]) cylinder(r=radius, h=len, center=true);
}