3D printing deisign applications that actually work?

[Roxy]

And just because I believe in helping people learn to help themselves...

Try this code:

$fn=100;
difference() {
cube([20,12,205]);
translate([10,12,193.5]) rotate([90,0,0]) cylinder(d=7, h=13);
translate([10,12,12.5]) rotate([90,0,0]) cylinder(d=7, h=13);
translate([10,12,12.5]) rotate([90,0,0]) cube([15,15,15]);
}