translate([0, 0, width / 2]){
tread(radius, tread_radius);}}
linear_extrude(height = qr_height){
difference (){
square(qr_size, center = true);
translate([0, 0, width / 2]){
tread(radius, tread_radius);}}
linear_extrude(height = qr_height){
difference (){
square(qr_size, center = true);