sxy = pi_nom_sz/2 - [1,1] * pi_nom_centres_in;
for (mx=[0,1]) mirror([mx,0,0]) for (my=[0,1]) mirror([0,my,0]) {
difference(){
sxy = pi_nom_sz/2 - [1,1] * pi_nom_centres_in;
for (mx=[0,1]) mirror([mx,0,0]) for (my=[0,1]) mirror([0,my,0]) {
difference(){