//Disable $fn and $fa, do not change these $fn=0; $fa=0.01; $fs=0.5; top_outer=25; top_inner=23.5; top_length=2; top_length2=2; difference() { union() { translate([0,0,top_length-top_length2])cylinder(top_length2,d=top_outer); } cylinder(top_length,d=top_inner); }