difference()
{
 hull()
    {
 cylinder(d=10,h=12,$fn=100);   
 translate([85,0,0]) cylinder(d=10,h=12,$fn=100);  
 translate([85,30,0]) cylinder(d=10,h=12,$fn=100);  
 translate([0,30,0]) cylinder(d=10,h=12,$fn=100);  
    }
    
    
  translate([1,1,1])   hull()
    {
 cylinder(d=10,h=12,$fn=100);   
 translate([83,0,0]) cylinder(d=10,h=12,$fn=100);  
 translate([83,28,0]) cylinder(d=10,h=12,$fn=100);  
 translate([0,28,0]) cylinder(d=10,h=12,$fn=100);  
    }
    
    
   translate([-10,7,4])  cube([10,10,8]);

}