//double pipe
$fn=1000;
difference() {
   cylinder( r1=150,r2=150,h=1000);
    
cylinder( r1=140,r2=140,h=1001);


}
difference() {
   cylinder( r1=75,r2=75,h=1000);
    
cylinder( r1=65,r2=65,h=1001);


}