diff --git a/include/short.scad b/include/short.scad
index 717a4549104e6a5c4b5138cfc28283337b2fcb2b..b7854e6f08bc76ce2ee1a8c161e7fa4afc6bc0df 100644
--- a/include/short.scad
+++ b/include/short.scad
@@ -38,3 +38,12 @@ module tube(l, th) {
         children();
     }
 }
+
+// produce a flat ring
+// parameters: outer diameter, thickness
+module ring(od, th) {
+    difference() {
+        circle(d = od);
+        circle(d = od - th*2);
+    }
+}