diff --git a/build123d/hexagon.py b/build123d/hexagon.py
index 6defe4c..8fb8490 100644
--- a/build123d/hexagon.py
+++ b/build123d/hexagon.py
@@ -14,7 +14,11 @@
 TRAPEZ_Z_LEN = 18
 TRAPEZ_TIP = 2.2
 
-TABS_Z_LEN = 4
+ALIGN_TAB_Z_LEN = 4
+
+FIT_TAB_RADIUS = 1.6
+FIT_TAB_X = 8
+FIT_TAB_Z = 2
 
 
 with BuildPart() as chex:
@@ -54,19 +58,27 @@
                 mirror(about=Plane.YZ)
             make_face()
         extrude(amount=TRAPEZ_THICKNESS/2, both=True)
+        # Fit tabs.
+        with Locations((FIT_TAB_X, 0, FIT_TAB_Z)):
+            Sphere(FIT_TAB_RADIUS)
+        with Locations((-FIT_TAB_X, 0, FIT_TAB_Z)):
+            Sphere(FIT_TAB_RADIUS)
+    # Place Trapezoid instances.
     with Locations((0, 0, BASE_Z_LEN)):
         add(trapezoid_pt, rotation=(0, 0, -45))
         add(trapezoid_pt, rotation=(0, 0, 45))
 
-    # Tabs (to prevent wrong insertion).
-    tab_z = TRAPEZ_Z_LEN - TABS_Z_LEN
+    # Align Tabs (to prevent wrong insertion).
+    tab_z = TRAPEZ_Z_LEN - ALIGN_TAB_Z_LEN
     normal = Axis(origin=(0,0,0), direction=(1,1,0))
     face1 = (chex.faces()
-        .filter_by(normal)[1]
+        .filter_by(normal)
+        .sort_by(Axis.Y)[1]
         .split(Plane.XY.offset(tab_z), keep=Keep.TOP)
     )
     face2 = (chex.faces()
-        .filter_by(normal)[3]
+        .filter_by(normal)
+        .sort_by(Axis.Y)[2]
         .split(Plane.XY.offset(tab_z), keep=Keep.TOP)
     )
     extrude(face1, until=Until.NEXT, dir=(0,1,0))