diff --git a/dims.scad b/dims.scad
index 2bc7f50..bc81e4f 100644
--- a/dims.scad
+++ b/dims.scad
@@ -3,7 +3,7 @@
 
 in2mm = 25.4;
 otod = in2mm * 5 / 2;
-otid = in2mm * 9 / 4;
+otid = in2mm * 9 / 4 + 1;
 itod = in2mm * 3 / 4;
 itid = in2mm * 5 / 8;
 itcr = 1;