diff --git a/polyholes.scad b/polyholes.scad
index 86f90cc..3e86a83 100644
--- a/polyholes.scad
+++ b/polyholes.scad
@@ -2,22 +2,28 @@
 // This file is licensed under the terms of Creative Commons Attribution 3.0 Unported.
 
 // Using this holes should come out approximately right when printed
-module polyhole(h, d) {
-	n = max(round(2 * d),3);
-	rotate([0,0,180])
-		cylinder(h = h, r = (d / 2) / cos (180 / n), $fn = n);
+module polyhole(h, d=0, r=0, center=false) {
+    _r = (r == 0 ? d / 2 : r);
+    _d = (d == 0 ? r * 2 : d);
+
+    n = max(round(2 * _d),3);
+
+    rotate([0,0,180])
+        cylinder(h = h, r = (_d / 2) / cos (180 / n), $fn = n, center=center);
 }
 
 module test_polyhole(){
-	difference() {
-		cube(size = [100,27,3]);
-		for(i = [1:10]) {
-			translate([(i * i + i)/2 + 3 * i , 8,-1])
-				polyhole(h = 5, d = i);
-			d = i + 0.5;
-			translate([(d * d + d)/2 + 3 * d, 19,-1])
-				polyhole(h = 5, d = d);
-		}
-	}
-}
+difference() {
+    cube(size = [100,27,3]);
+    union() {
+        for(i = [1:10]) {
+            translate([(i * i + i)/2 + 3 * i , 8,-1])
+                polyhole(h = 5, d = i);
 
+            assign(d = i + 0.5)
+                translate([(d * d + d)/2 + 3 * d, 19,-1])
+                    polyhole(h = 5, d = d);
+        }
+    }
+}
+}