diff --git a/nhf/joints.py b/nhf/joints.py
index f809989..554d7b6 100644
--- a/nhf/joints.py
+++ b/nhf/joints.py
@@ -13,6 +13,7 @@ def hirth_joint(radius=60,
     """
     # ensures secant doesn't blow up
     assert n_tooth >= 5
+    assert radius > radius_inner
 
     # angle of half of a single tooth
     theta = math.pi / n_tooth
@@ -64,7 +65,7 @@ def hirth_joint(radius=60,
             radius=radius,
             centered=(True, True, False))
         .faces(">Z").tag("bore")
-        .union(teeth.val().move(Cq.Location((0,0,base_height))))
+        .union(teeth.val().move(Cq.Location((0,0,base_height))), tol=tol)
         .clean()
     )
     #base.workplane(offset=tooth_height/2).circle(radius=radius,forConstruction=True).tag("mate")
diff --git a/nhf/touhou/houjuu_nue/__init__.py b/nhf/touhou/houjuu_nue/__init__.py
index c4813ee..8d2c0c8 100644
--- a/nhf/touhou/houjuu_nue/__init__.py
+++ b/nhf/touhou/houjuu_nue/__init__.py
@@ -1,6 +1,7 @@
 from dataclasses import dataclass
 import unittest
 import cadquery as Cq
+import nhf.joints
 
 @dataclass(frozen=True)
 class Parameters:
@@ -25,6 +26,75 @@ class Parameters:
     wing_r2_height = 100
     wing_r3_height = 100
 
+    """
+    The Houjuu-Scarlett joint mechanism at the base of the wing
+    """
+    hs_joint_base_width = 85
+    hs_joint_base_thickness = 10
+    hs_joint_ring_thickness = 10
+    hs_joint_tooth_height = 10
+    hs_joint_radius = 30
+    hs_joint_radius_inner = 20
+    hs_joint_corner_fillet = 5
+    hs_joint_corner_cbore_diam = 12
+    hs_joint_corner_cbore_depth = 12
+    hs_joint_corner_diam = 15
+    hs_joint_corner_inset = 15
+
+    def print_geometries(self):
+        return [
+            self.hs_joint_parent()
+        ]
+
+    def hs_joint_parent(self):
+        """
+        Parent part of the Houjuu-Scarlett joint, which is composed of a Hirth
+        coupling, a cylindrical base, and a mounting base.
+        """
+        hirth = nhf.joints.hirth_joint(
+            radius=self.hs_joint_radius,
+            radius_inner=self.hs_joint_radius_inner,
+            tooth_height=self.hs_joint_tooth_height,
+            base_height=self.hs_joint_ring_thickness)
+        hole_rect_width = self.hs_joint_base_width - 2 * self.hs_joint_corner_inset
+        hirth = (
+            hirth
+            .faces("<Z")
+            .workplane()
+            .transformed(
+                offset=Cq.Vector(0, 0, -self.hs_joint_ring_thickness / 2),
+                rotate=Cq.Vector(90, 0, 0))
+            # This hole will drill only to the centre and not through. This is
+            # intended.
+            .hole(5)
+            .val()
+        )
+        result = (
+            Cq.Workplane('XY')
+            .box(
+                self.hs_joint_base_width,
+                self.hs_joint_base_width,
+                self.hs_joint_base_thickness,
+                centered=(True, True, False))
+            .edges("|Z")
+            .fillet(self.hs_joint_corner_fillet)
+            .faces(">Z")
+            .workplane()
+            .rect(hole_rect_width, hole_rect_width, forConstruction=True)
+            .vertices()
+            .cboreHole(
+                diameter=self.hs_joint_corner_diam,
+                cboreDiameter=self.hs_joint_corner_cbore_diam,
+                cboreDepth=self.hs_joint_corner_cbore_depth)
+            .faces(">Z")
+            .workplane()
+            .union(hirth.move((0, 0, self.hs_joint_base_thickness)), tol=0.1)
+            .clean()
+        )
+        return result
+
+
+
     def wing_r1_profile(self) -> Cq.Sketch:
         """
         Generates the first wing segment profile, with the wing root pointing in