diff --git a/nhf/joints.py b/nhf/joints.py
index 9cdd0ad..02c7527 100644
--- a/nhf/joints.py
+++ b/nhf/joints.py
@@ -99,10 +99,139 @@ def hirth_assembly():
     )
     return result
 
+def comma_joint(radius=30,
+                shaft_radius=10,
+                height=10,
+                flange=10,
+                flange_thickness=25,
+                n_serration=16,
+                serration_angle_offset=0,
+                serration_height=5,
+                serration_inner_radius=20,
+                serration_theta=2 * math.pi / 48,
+                serration_tilt=-30,
+                right_handed=False):
+    """
+    Produces a "o_" shaped joint, with serrations to accomodate a torsion spring
+    """
+    assert flange_thickness <= radius
+    flange_poly = [
+        (0, radius - flange_thickness),
+        (0, radius),
+        (flange + radius, radius),
+        (flange + radius, radius - flange_thickness)
+    ]
+    if right_handed:
+        flange_poly = [(x, -y) for x,y in flange_poly]
+    sketch = (
+        Cq.Sketch()
+        .circle(radius)
+        .polygon(flange_poly, mode='a')
+        .circle(shaft_radius, mode='s')
+    )
+    serration_poly = [
+        (0, 0), (radius, 0),
+        (radius, radius * math.tan(serration_theta))
+    ]
+    serration = (
+        Cq.Workplane('XY')
+        .sketch()
+        .polygon(serration_poly)
+        .circle(radius, mode='i')
+        .circle(serration_inner_radius, mode='s')
+        .finalize()
+        .extrude(serration_height)
+        .translate(Cq.Vector((-serration_inner_radius, 0, height)))
+        .rotate(
+            axisStartPoint=(0, 0, 0),
+            axisEndPoint=(0, 0, height),
+            angleDegrees=serration_tilt)
+        .val()
+    )
+    serrations = (
+        Cq.Workplane('XY')
+        .polarArray(radius=serration_inner_radius,
+                    startAngle=0+serration_angle_offset,
+                    angle=360+serration_angle_offset,
+                    count=n_serration)
+        .eachpoint(lambda loc: serration.located(loc))
+    )
+    result = (
+        Cq.Workplane()
+        .add(sketch)
+        .extrude(height)
+        .union(serrations)
+        .clean()
+    )
+
+    result.polyline([
+        (0, 0, height - serration_height),
+        (0, 0, height + serration_height)],
+        forConstruction=True).tag("serrated")
+    result.polyline([
+        (0, radius, 0),
+        (flange + radius, radius, 0)],
+        forConstruction=True).tag("tail")
+    result.faces('>X').tag("tail_end")
+    return result
+
+def torsion_spring(radius=12,
+                   height=20,
+                   thickness=2,
+                   omega=90,
+                   tail_length=25):
+    """
+    Produces a torsion spring with abridged geometry since sweep is very slow in
+    cq-editor.
+    """
+    base = (
+        Cq.Workplane('XY')
+        .cylinder(height=height, radius=radius,
+                  centered=(True, True, False))
+    )
+    base.faces(">Z").tag("mate_top")
+    base.faces("<Z").tag("mate_bottom")
+    result = (
+        base
+        .cylinder(height=height, radius=radius - thickness, combine='s',
+                  centered=(True, True, True))
+        .transformed(
+            offset=(0, radius-thickness),
+            rotate=(0, 0, 0))
+        .box(length=tail_length, width=thickness, height=thickness, centered=False)
+        .copyWorkplane(Cq.Workplane('XY'))
+        .transformed(
+            offset=(0, 0, height - thickness),
+            rotate=(0, 0, omega))
+        .center(-tail_length, radius-thickness)
+        .box(length=tail_length, width=thickness, height=thickness, centered=False)
+    )
+
+    return result
+
+def comma_assembly():
+    joint1 = comma_joint()
+    joint2 = comma_joint()
+    spring = torsion_spring()
+    result = (
+        Cq.Assembly()
+        .add(joint1, name="joint1", color=Cq.Color(0.8,0.8,0.5,0.3))
+        .add(joint2, name="joint2", color=Cq.Color(0.8,0.8,0.5,0.3))
+        .add(spring, name="spring", color=Cq.Color(0.5,0.5,0.5,1))
+        .constrain("joint1?serrated", "spring?mate_bottom", "Plane")
+        .constrain("joint2?serrated", "spring?mate_top", "Plane")
+        .constrain("joint1?tail", "FixedAxis", (1, 0, 0))
+        .constrain("joint2?tail", "FixedAxis", (-1, 0, 0))
+        .solve()
+    )
+    return result
+
 class TestJoints(unittest.TestCase):
 
     def test_hirth_assembly(self):
         hirth_assembly()
+    def test_comma_assembly(self):
+        comma_assembly()
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/nhf/touhou/houjuu_nue/__init__.py b/nhf/touhou/houjuu_nue/__init__.py
index f91d538..8eac42c 100644
--- a/nhf/touhou/houjuu_nue/__init__.py
+++ b/nhf/touhou/houjuu_nue/__init__.py
@@ -1,17 +1,34 @@
 import cadquery as Cq
+from dataclasses import dataclass
 
-def mystery():
-    return (
-        Cq.Workplane()
-        .box(1, 1, 1)
-        .tag("base")
-        .wires(">Z")
-        .toPending()
-        .translate((0.1, 0.1, 1.0))
-        .toPending()
-        .loft()
-        .faces(">>X", tag="base")
-        .workplane(centerOption="CenterOfMass")
-        .circle(0.2)
-        .extrude(3)
-    )
+@dataclass(frozen=True)
+class Parameters:
+
+    """
+    Thickness of the exoskeleton panel in millimetres
+    """
+    panel_thickness: float = 25.4 / 16
+
+    # Wing root properties
+    """
+    Radius of the mounting mechanism of the wing root. This is constrained by
+    the size of the harness.
+    """
+    root_radius: float = 60
+
+    def wing_root(self,
+                  side_width=30,
+                  side_height=100):
+        """
+        Generate the wing root which contains a Hirth joint at its base and a
+        rectangular opening on its side, with the necessary interfaces.
+        """
+        result = (
+            Cq.Workplane("XY")
+            .circle(self.root_radius)
+            .transformed(offset=Cq.Vector(80, 0, 80),
+                         rotate=Cq.Vector(0, 45, 0))
+            .rect(side_width, side_height)
+            .loft()
+        )
+        return result