union(){
difference(){
cylinder(6,13,13, $fn=100);
    translate([0,0,2])cylinder(6,10.2,10.2, $fn=100);  
}
translate([0,0,6.5])cube([26,2,2], center=true);
translate([0,0,6.5])rotate (90,0,0) cube([26,2,2], center=true);
}