diff --git a/CFTubes.scad b/CFTubes.scad
index 262eec8..d601356 100644
--- a/CFTubes.scad
+++ b/CFTubes.scad
@@ -166,7 +166,7 @@ module headpiece(string_spacing=18, string_margin=4.5, num_strings=3, target_nec
 				linear_extrude(headpiece_length)
 				polygon([for (i = [0:300]) let(a=lerp(a0, a1, i/300.0)) [neck_width*0.5*sin(a), -target_neck_thickness*cos(a)]]);
 	}
-	module string_tubes() {
+	module string_tubes(tolerance = 1.0) {
 		string_thicknesses = [4.9, 4.2, 3.0];
 		module string_tube(diameter, fn=36) {
 			hole_r = diameter/2;
@@ -185,7 +185,7 @@ module headpiece(string_spacing=18, string_margin=4.5, num_strings=3, target_nec
 			}
 		};
 		for (i = [0:num_strings-1]) {
-			string_diameter = string_thicknesses[i];
+			string_diameter = string_thicknesses[i] + tolerance;
 			x = -neck_width/2 + string_margin + (i*string_spacing);
 			translate([x, x0+2, -target_neck_thickness+scallop_depth+fw2]) string_tube(string_diameter);
 		}